how to separate gold, silver and platinum? reclaim, recycle, and sell your precious metal scrap

how to separate gold, silver and platinum? reclaim, recycle, and sell your precious metal scrap

We have written before about burning materials, or exposing them to very high heat, as a way to extract the gold, silver, platinum and other metals they contain. Today, lets review and also tell you about some additional materials that can be processed in this way by a qualified precious metals refinery like ours.

The philosophy and process is simple. When you take a material that contains a mixture of metals and non-metallic substances, you can use heat to literally burn off those additional substances, leaving only the metal behind. Incidentally, we are not writing todays post to recommend that you burn materials of different kinds so you can separate gold, silver, and platinum from them. We are writing to raise your consciousness about different materials that you should send to us for processing. Why shouldnt you burn these materials yourself in your kitchen or garage or basement? Its because the secondary materials that they contain could be toxic and can harm you.

If you have a quantity of thermocouple wire that contains silver and/or other precious metals, we can apply high heat to them to separate out the metals they contain. (Note that there will probably also be copper, sometimes tin, and other secondary metals.) And another thing when we expose some thermocouple wire to high heat, we also remove insulation that covers the thermocouples. The result, again, is that we can extract the silver and other precious metals they contain.

Lets say you have a quantity of floor sweepings that you collected at a jewelry factory. Those powdery materials might contain small flecks of gold, silver, and platinum scrap. The application of high heat causes those precious metals to separate and be left behind after dust, sawdust and other undesirable contents are reduced to ash. Give us a call at 800-426-2344 and we can explain how this works.

Sometimes a rug that was on the floor of a jewelry factory contains embedded gold powders that can be separated by literally burning. The same is sometimes true for an apron that a jeweler wore when fabricating jewelry. (Sometimes gold and silver and platinum dust have collected on the bottoms of pockets.) Again, give us a call and we can explain the process to you.

Printed circuit boards from virtually any kind of electronic devices can contain gold and silver, as well as lead or silver-based solder, copper, and of course plastic that will melt and fall away when the board is exposed to high heat.

These materials, which were once used in vast quantities, are now outmoded. But large quantities of them can still be found in photo labs, hospitals, and medical testing facilities. You can burn them to separate the silver they contain. Note that in some cases, immersing films and papers in acid can dissolve the non-metallic materials they contain, leaving the precious metals behind.

As we have noted before on this blog, gold-leaf-covered wooden frames usually contain extremely small quantities of gold. Separating that gold is usually not worth the effort and expense. However, lets pause for a moment to observe that if a gold-leaf-covered frame (or other wooden item) is burned, the gold is left behind. So if you happen to have a large quantity of old gold wooden items like picture frames, or architectural moldings from a church, it could be worth extracting the gold they contain. Give us a call to learn more.

In years past, small items of jewelry sometimes were made of gold that had silver appliqued to their surfaces. We have seen a variety of such items, including the slip-on cases that were used on cigarette lighters, items of barware, and more. If you have old items like those, do give us a call at 800-426-2344 and talk to us. Heat can be your best friend when it comes to separating the gold from other materials these items contain.

separating the platinum group metals by liquidliquid extraction | johnson matthey technology review

separating the platinum group metals by liquidliquid extraction | johnson matthey technology review

To extract the platinum group metals from the ore, and to refine them to the very high purity required for their many applications, requires a multitude of complex operations. At present the final refining stage that produces the individual platinum group metals is carried out by selective precipitation from a solution of mixed platinum group metals, but this is inefficient as far as the degree of separation is concerned. An improved process which makes use of liquidliquid extraction has been developed to a pilot plant stage, and this paper highlights some of the chemical and process principles that underlie this method of separation.

The platinum group metals platinum, palladium, rhodium, iridium, osmium and ruthenium together with silver and gold generally occur in nature associated with the major base metals iron, copper, nickel and cobalt and a wide range of minor elements such as lead, tellurium, selenium and arsenic, and both technical and commercial considerations demand that the individual platinum group metals be separated from the other metals and from each other to high purity, with high yield and with a high percentage recovery.

Current refining processes are based on complex selective precipitation techniques, and these are often inefficient in terms of the separation efficiency achieved. Interfering elements can be co-precipitated, and filter cakes often contain entrained filtrate. Thorough washing of these cakes is difficult to achieve owing to their nature, and their structure, and they often have poor filtration characteristics. Processing is therefore complex, and repeated washing and filtration cycles are required, as each stage generates recycles and residues requiring recovery.

The large and complex recycles that are necessary result in low primary yields. The nature of the process, and the problems associated with corrosion and the engineering of these filtration and cake handling stages, makes plant unreliable, complicated and labour intensive.

Recognition of the problems associated with current technology led Johnson Matthey and Matthey Rustenburg Refiners to embark on a research and development programme during the 1970s to examine potential alternative refining technology. Several alternatives were examined and liquidliquid extraction was identified as a technique capable of giving the desired separation characteristics, and satisfying the process constraints.

Generally several requirements exist for a refining process, and major criteria include the avoidance of precipitates, high separation efficiency of the desired element, and good selectivity for the desired element.

Liquid-liquid extraction supplies these; as a technique it has long been recognised in the sphere of analytical chemistry. Industrial applications are more recent and are increasingly employed in the non-precious metals industry, for example during the extraction of uranium, plutonium, zirconium, hafnium, the rare earths, copper, cobalt and nickel. Currently liquidliquid extraction is employed commercially by Matthey Rustenburg Refiners for the separation of copper, cobalt and gold.

The separation relies on the desired metal being selectively extracted from the aqueous phase by an immiscible organic solvent. It is often forgotten, but equally important, that the metal must also be capable of back-extraction with another suitable aqueous phase. The organic and aqueous phases used must be compatible with process, health and safety, and cost considerations.

This applies at a given set of conditions for the system and is an equilibrium relationship, which is usually a constant for dilute solutions. However, in commercial systems solutions are not dilute and solvents have only a limited capacity for extracting metal. A typical plot is shown in Figure 1.

The process chemistry is the key to separation (1). It must allow separation of the platinum group metals from the base metals, where the major difference is in complex formation, and also separation of individual platinum group metals from each other, to a high degree of purity.

The chloride system provides the most effective operating medium for platinum group metals and is widely used. The separation process chemistry considered here is therefore based on this system. The normal platinum group metals species encountered are shown in Table I. These species can aquate in weak chloride solutions and water, but this is inhibited in stronger chloride media. Platinum group metal complexes are generally much more stable than the equivalent base metal complexes and this allows platinum group metals/base metals separation. Complexes containing the heavier donor atoms are more stable and the following overall order applies:

Although sulphur bonded systems have been used, and they give excellent distribution coefficients, the kinetics of the reaction are slow and the reverse reaction, stripping, is usually difficult. The chloride system, while having less favourable, but nonetheless acceptable, extraction characteristics, gives the good overall extract-strip balance required for a commercial process.

With compound formation extractants can be chelating agents, carboxylic or sulphonic acids, or acidic organophosphorus compounds. Important in this class are the oxime reagents. Substitution kinetics for the platinum group metals, for example platinum or palladium, are relatively slow compared to base metals such as copper. A generalised form of this reaction is:

Various schemes can be postulated for extracting both primary and secondary materials, depending on starting feedstock and process constraints. Following dissolution, gold is usually removed at an early process stage, and is therefore considered first.

Solvent extraction for gold is well known (2) and has been commercially operated for a number of years. Extraction as the [AuCl4] ion with solvating reagents such as methyl iso-butyl ketone (MIBK) or dibutyl carbitol (Butex) is rapid and efficient. The gold is recovered as metal by direct reduction of the organic phase, following scrubbing to remove co-extracted impurities.

Platinum can be removed, in the absence of palladium and gold, by ion exchange if iridium is in the Ir(III) oxidation state. This is illustrated in Figure 2 which shows the distribution of a range of platinum group metal chloroanions with tri-n-octyl amine. The reaction below lies well to the right.

Palladium extraction systems based on both long chain alkyl sulphides (3) and hydroxyoximes have been reported in recent years. Oximes are produced commercially and widely available, particularly for copper extraction from leach liquors. These oximes have high distribution coefficients for palladium but suffer from slow reaction kinetics. To overcome this, new accelerating additives based on organic amines and other organic compounds containing sulphur, phosphorus and arsenic are used. When these are coupled with a novel design of extractor they permit continuous commercial operation.

Ruthenium and osmium extraction from chloro species is difficult owing to the complex series of equilibria that exist in solution. The removal of ruthenium and osmium as tetroxides using distillation or carbon tetrachloride extraction, or extraction as [RuNOCl5]2 with anion exchangers (4) have been reported.

Iridium can be oxidised to Ir(IV) and then removed with platinum as illustrated in Figure 2, once palladium and gold have been removed. Equally if iridium remains as Ir(III), platinum can be extracted leaving iridium in solution. It can then be oxidised to Ir(IV) and extracted. This ability to select iridium extraction by control of the iridium oxidation state gives great flexibility to the separation process. Amine solvents are preferred and extraction is similar to that for platinum. A high Cl concentration suppresses extraction of rhodium and co-extracted impurities are removed by an acid scrub stream.

Mixer settlers are widely used as discrete stage contactors. The two phases are first mixed in a chamber, the size of which is determined by consideration of the reaction kinetics of the process. A typical unit is illustrated in Figure 3. The unit is fed continuously and the dispersed phase flows into the settling chamber. This must be sized such that the settler is not flooded with dispersion. The dispersion-band thickness depends on several parameters such as mixing conditions, flowrates, phase continuity, and organic and aqueous phase composition. A typical curve showing the variation of dispersion band thickness with flowrate is shown in Figure 4.

The thickness of the dispersion band depends on a number of factors including the mixing conditions, the composition of the phases and the flowrates. This curve shows the variation in thickness with flowrate

Not all of the desired metal is extracted in a single equilibrium contact, and several stages are usually needed. Also a practical stage is usually only about 90 per cent efficient. The number of actual stages required is derived from knowledge of the equilibrium curve as shown in Figure 1, and of the efficiency and flowrate conditions required. This is shown graphically in Figure 5. It can be demonstrated that the operating line has a slope equal to the phase flow ratio in the cascade. Mixer settlers can be readily banked into multi-stage units to give the desired flowsheet configuration.

Not all of the desired metal is extracted in a single equilibrium contact and several stages may be required, the number being derived from a knowledge of the equilibrium curve and the efficiency and flowrate conditions

The cascade is operated with countercurrent aqueous and solvent flow. Both pump mix units, generally favoured by the copper industry, and hydraulic flow units favoured by the nuclear industry are used at appropriate locations.

Columns can also be used for operation. They are less flexible than mixer settlers and are limited to systems with fast kinetics and phase separation characteristics, needing relatively few theoretical stages.

Following the research by Johnson Matthey and development with pilot plant operation of this process at the Matthey Rustenburg Refiners (UK) Limited, Royston Refinery, Matthey Rustenburg Refiners has recently announced its decision to erect a Solvex production refinery on the Royston site (5).

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metallurgy - how were silver and gold separated using the salt cementation process? - chemistry stack exchange

metallurgy - how were silver and gold separated using the salt cementation process? - chemistry stack exchange

Stack Exchange network consists of 177 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Gold and silver are often extracted from the same ores and are difficult to separate due to their chemical similarity, which prevents the use of techniques such as cupellation. Acid-based methods were discovered during the medieval period but were too expensive for use, so the main method of gold parting (the separation of gold from other metals) until the C16th was by salt cementation, in which sheets or granules of low-purity gold were heated with salt (NaCl) and/or other other compounds.

I would like to understand how this process was actually used. Wikipedia says the silver chloride (AgCl) produced is 'removed' but does not describe how. It also mentions that AgCl is volatile and the vessel used for the process is sealed to prevent its escape, which seems to contradict the previous statement. At the same time, it mentions the process is kept below 1000degC to stop the gold from melting, which is a long way below the boiling point of AgCl at atmopsheric pressure (although I don't know what pressure would be reached inside the vessel or how that would affect the volatility of AgCl). Furthermore, I thought that upon heating AgCl would normally decompose to silver (and chlorine) anyway, which in a simple, sealed vessel would presumably just remix with the gold. Some sort of alembic arrangement, maybe? I'm pretty sure I've misunderstood something fairly basic here.

I'm then further confused by this 1974 paper by Notton (open access) which seems to describe a recreation of what sounds like salt cementation process but then compares it to cementation (meaning it must differ significantly in some way I'm missing), and also sheds no light on the mechanism for recovering silver, although notes that the alumina plug of the sealed container ends up discoloured by silver salts after heating. Were the silver salts absorbed by the walls of the container, as in lead/silver cupellation?

M. Berthelot gives it from Papyrus V from the Leyden Papyrus X, in his Introduction l'tude de le Chimie, des anciens et du moyen ge (Introduction to the study of Chemistry, of forefathers and the middle age). The papyrus is at least from the III century, the process very probably older. From page 14 (my translation):

"Take piquant vinegar, thicken, take some [lacuna], 8 drachmas of common salt, 2 drachmas of lamellar alum (schist), 4 drachmas of litharge, crush with vinegar for 3 days, separate by decantation and employ. Then add to the vinegar 1 drachma of copperas, half an obole(1) of [lacuna], 3 oboles of chalcite(2), one and a half oboles of sory(3), one silique(4) of common salt, two siliques of Cappadoce salt(5). Make a lamella having two quarters (of an obole?) Submit it to the acion of fire... until the lamella breaks, then take the pieces and view them as refined gold.

"First prepare a cement composed of 4 parts crushed bricks passed on a sieve, one part green vitriol calcined to red, and one part common salt: mixe the whole very-exactly, and make a firm paste, moistening it with a little water or urine. This cement is called cment royal, because it is used to purify gold, which chemists view as the king of metals.

On the other hand, reduce the gold one wishes to prepare, to lamellas about as thin as billon pieces: at the bottom of a crucible or cementation pot, place a layer of the cement of thickness the width of a finger: stratify the gold lamellas on this layer: place on top a new layer of cement: thus fill the pot, always placing the gold between two layers of cement; and cover it with a lid sealed with sand and clay. Place the pot in a furnace or oven ; heat progressively, until the pot is a dull red ; maintain this level of heat for about twenty four hours: it is very-essential that the heat not be able to melt the gold. After that, let the pot cool down, and open it to remove the gold, which must be separated thouroughly from the surrounding cement: it also has to be boiled in large quantities pure water several times. One can try this gold on a touchstone or otherwise ; and if it is found insufficiently pure, submit it a second time to the process.

The vitriolic acid of the brick and of the calcined vitriol, releases the acid from the common salt during this cementation ; and this last one dissolves the silver alloyed to the gold, and seperates it by this mean.

By proceeding thus, the silver and other metals dissolve in the sodium chloride, with the help of the oxidative -- and then chlorinating -- action exerted by the iron oxide derived from the vitriol ; while the gold remains unchanged.

So what I think happens is: the silver reacts with $\ce{Cl2}$ and maybe $\ce{FeCl2}$ (speculation?, b.p.= 1023C, vapor pressure at 800C = 0.1bar) to give $\ce{AgCl}$. Then the $\ce{AgCl}$ evaporates (b.p.= 1547C, vapor pressure at 800C = 0.1mbar), condensates on the cement, and dissolves in it. It is unclear whether the silver stays in oxidized form. I would bet yes, but I am no inorganic chemist.

Concerning this silver, it can subsequently be separated from the cement, by heating it with a sufficient quantity of lead and litharge, and taking the resulting silver containing lead slag and cupelating it to remove the lead."

He then adds that you can add both common salt and saltpeter, and not only does the silver still get dissolved, the gold doesn't. Which is also weird because you have all the components of aqua regia, but it doesn't attack the gold. Macquer does acknowledge his low confidence in his sources for this last process.

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how to separate precious metal

how to separate precious metal

A wide variety of different types of electronics and other household objects contain at least one type of precious metal. In many cases, the trace amounts of these metals are fused together inside of the object. In order to recover those metals once the object has worn out or broken, you'll need to properly know how to separate the metal. Adsorption, a process of separating out metal solids from liquid solutions, is common, as is smelting, a process that removes different types of metals from one another. Read on for a brief guide on separating out the most common type of precious metal at home.

Ensure that you know exactly how to safely operate your tilting furnace. Be sure to also wear any protective equipment that is necessary prior to using the furnace. When you're ready, insert the circuit into the furnace and begin to heat the furnace. Monitor the temperature inside the furnace closely, and allow it to continue to heat up until the temperature inside of the furnace is approximately 1200 degrees C (or about 2192 degrees F).

The "slag" is the liquid metal mixture that will be the result of the temperature being raised to the high level that it is. To create the slag, you'll need to mix in the silica and the sodium borate chemicals into the furnace and on top of the gold-plated circuit. Do this according to the usage instructions of your particular furnace and ensure that you remain safe at all times. The silica and sodium borate are collectively known as "fluxes" in this procedure.

The slag will not develop instantly. Rather, it will take about an hour and a half for the metals to dissolve. If the metals have not dissolved completely during this time, raise the temperature of the furnace to about 1400 degrees C (or about 2552 degrees F).

Continue to heat the slag until you can observe the molten gold begin to dissolve away from the rest of the slag. This occurs because of the melting point and the density of the gold as compared with the different melting points and densities of the other metal components of the slag. The gold should slip down into the smelting vessel.

After this occurs, you can cool and remove the gold from the smelting vessel and also remove the slag as well. It's common at this point to refine the gold through a separate refinement process to ensure a high level of purity. For more information on refinement procedures of this type, consult with a blacksmith or an experienced smelter in your area.

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froth flotation method - jxsc machine

froth flotation method - jxsc machine

The Froth Flotation Method is means separating minerals according to their different physical and chemical properties. According to classification, the flotability of gold and silver minerals is included in the first category of natural and non-ferrous heavy metal sulfides, characterized by low surface wettability and easy flotation, which can be flotation by xanthate collectors.

The froth flotation method is widely used to treat various veins of gold and silver ores for the following reasons: (1) In most cases, the froth flotation process can enrich gold and silver in sulfide concentrate to the greatest extent and discard a large number of tailings, thus reducing the smelting cost. (2) When the flotation machine is used to treat polymetallic gold and silver ores, concentrates containing gold, silver and non-ferrous heavy metals can be effectively separated, which is conducive to the comprehensive utilization of valuable mineral resources. (3) For refractory gold and silver ores which cannot be treated directly by mercury amalgamation or cyanidation, a combined process including flotation is needed. However, there are some limitations in flotation, such as ores with gold particles larger than 0.2-0.3 mm or pure quartz gold ores without metal sulfides, which are difficult to deal with by flotation separation alone.

parting | metallurgy | britannica

parting | metallurgy | britannica

Parting, in metallurgy, the separation of gold and silver by chemical or electrochemical means. Gold and silver are often extracted together from the same ores or recovered as by-products from the extraction of other metals. A solid mixture of the two, known as bullion, or dor, can be parted by boiling in nitric acid. The silver is dissolved as silver nitrate, leaving a residue of gold that is filtered off and washed; silver is precipitated out of solution by the addition of ferrous sulfate. This is the traditional method used in assaying the content of gold and silver samples.

Most gold and silver are parted electrolytically after being recovered in the slimes left over from copper refining or as a metallic by-product of lead or zinc smelting. The bullion is cast into anodes, which are placed into an electrolytic cell and subjected to an electric current. Silver dissolves in the electrolyte and then deposits onto the cathodes. Gold and trace amounts of silver are recovered in the slimes and are parted either electrolytically or by boiling in sulfuric acid and potassium nitrate to dissolve the silver.

separating platinum from gold during the early eighteenth century | johnson matthey technology review

separating platinum from gold during the early eighteenth century | johnson matthey technology review

Following the discovery of platinum in the Viceroyalty of New Granada at the beginning of the 18th Century, its use to degrade gold forced the colonial authorities to improve their existing methods of separating and analysing the precious metals. Using information from the Royal Mint of Santa F de Bogot, the various ways of separating these metals are now considered, including the little-known method of inquartation.

Even before the discovery of the Americas by European explorers, elementary platinum metallurgy was apparently known to some of the indigenous population of the central region of New Granada; an area, shown alongside on a rare 18th century map, which was never fully integrated into the Inca world, and which now constitutes the southern part of Colombia and the northern part of Equador. Following the conquest of the New World by European invaders, however, this information appears to have been lost.

The somewhat late discovery of platina in the Choc area of the New Granada viceroyalty, during the 18th century, was due to several factors. This area had remained relatively isolated from Spanish penetration because of the mountainous terrain, high temperatures, heavy rainfall, numerous rivers and, above all, warlike inhabitants. For these reasons, the extraction of Chocan gold from placer deposits and gold-bearing veins did not begin until almost the 18th century, so it was only then that the existence of platina among the gold was recognised. Indeed the presence of platina in such an important gold mining region constituted a problem for both the miners and the colonial authorities.

However, platina could have been encountered as early as 1690, when the platiniferous area around Tad in the upper part of the San Juan river valley was first worked Its presence in the gold obtained from alluvial deposits would have been noted by the miners, by employees of the Nvita and Citar foundries, and by officials of the Royal Mints at the administrative centres of Popayan, Mariquita and Santa F de Bogot, where the gold was melted.

Soon gold was being degraded by the deliberate addition of platina, which was difficult to detect because of its similar density. Indeed the first written reference to platina noted that the mixing of platina and gold was banned (1).

This contamination required the colonial authorities to improve the existing methods of identifying platina and of separating it from the gold with which it occurred. Three methods were available: amalgamation, inquartation and melting. The inquartation method which was used at the beginning of the 18th century is not generally known today, although people are more aware of the other two processes.

The first information about platina to reach Europe was communicated by Antonio de Ulloa (17161795), in the famous Relacin Histrica (2). This was written as a result of the French-Spanish geodesic expedition, whose objective was to determine the shape of the earth. Following this event, scientific investigation of platinum started in Europe in 1748, at least half a century after some technical knowledge of it had existed in New Granada.

The occurrence of platina in the Viceroyalty of New Granada at the beginning of the 18th century, the legal and technical problems that it caused and the solutions provided at that time are not well known today. Therefore in this article we will examine the methods used at that time for the separation of platina from gold in Spanish America.

The amalgamation method of separation is based upon the fact that the solubility of the platinum group metals in mercury is low, while the solubility of gold is high. Platinum and palladium, the lower melting points metals in the platinum group, form intermetallic compounds with mercury. Both show slight solubility in mercury: 0.0008 and 0.2 weight per cent for platinum and palladium, respectively, at a temperature of 300C (3); although higher figures have been suggested for platinum: 0.1 and 0.2 weight per cent at 24 and 54C, respectively (4). The platinum group metals with the higher melting points, namely osmium, iridium and ruthenium, do not form intermetallic compounds with mercury as their solubility is very small (<105 weight per cent at 500C). Finally, rhodium shows a slightly higher solubility than these (6 105 weight per cent at 500C), but it does not form compounds with mercury (3).

At the end of the amalgamation process, the amalgams and any remaining mercury are separated from the insoluble waste by filtration through leather or various types of cloth, the degree of separation being determined by the pore size of the filtering medium (5). Thus, the amalgamation process would be better for separating osmium, iridium, ruthenium and rhodium than for platinum and palladium. However, all of them would, to some slight extent, form an amalgam with mercury and would therefore be recovered with the gold.

In Spanish America treatment with mercury was the usual means of isolating gold mined from mineral veins. The process was not necessary for gold recovered from placer deposits, as Bernabe Cobo (15821657) noted in his Historia del Nuevo Mundo (6):

In the Choc area the amalgamation process was carried out in shallow wooden or clay washing pans or trays (bateas), where the finely divided alloy was treated with mercury. After that, it was separated by passing the amalgam through filter cloths.

The recovery of gold from the amalgam was carried out by distillation in an improvised furnace containing two different sized bateas, arranged one above the other. A very hot flagstone with the amalgam upon it, was placed inside the furnace and then the volatilised mercury condensed on the upper batea and collected in the lower one, while the resulting gold remained on the stone (7).

The first known reference to the use of the amalgamation process to separate gold from platina appears in a report dated 1721 (8). It occurs in an account of a Tad judges inquiry, in which he points out that he had been present during a separation operation:

The gold was washed and cleaned in my presence with mercury and gave two hundred and fifty pounds and what appeared to be seven or eight pounds of platina. The latter took place in the presence of Captain Francisco Perea and witnesses who hereby confirm that it came from the San Juan river.

On many occasions this amalgamation process has been quoted as being the only method used for the separation of platina before a scientific interest in the platinum metals developed in Europe during the second half of the 18th century (9). However, this was erroneous.

In the same way as gold, the platinum group metals are very resistant to chemical reagents, including acids, bases and halogens. This is due to the thermodynamic stability of their crystalline structures and also to the formation of monoatomic layers of some oxides on the surface of the metals during the dissolution process, which renders them passive (10).

Nevertheless, the reactivity of the platinum group metals is largely determined by their degree of dispersion in other metals, as well as by the formation of intermetallic compounds. It also depends on the presence and type of impurities, particle size, metallurgical history and dissolution technique employed.

Therefore, one way of breaking up compact metals before dissolution is to alloy them with a more active metal. In this way the dispersion of the platinum group metals throughout the metal, or the formation of intermetallic compounds which are soluble in mineral acids, helps the dissolution process (11, 12). To assist in the dissolution of the platinum group metals, zinc (1316), tin (12, 17), bismuth (12) and silver (1826) have been used.

In the case being considered here, the separation is based on a ternary silver-gold-platinum alloy. In suitable proportions, this alloy is partially soluble in nitric acid which, of course, leaves gold undissolved. In consequence, the addition of the correct quantity of silver followed by treatment with nitric acid, will permit the separation of the gold-platinum alloy.

This method of separation, from now on referred to as the inquartation process, is very similar to the apartado method, which, during the time we are referring to, was used to separate gold and silver, and was based upon the selective dissolution of silver in nitric acid.

The inquartation method of separating gold and platinum was investigated in Europe by several scientists. The first of these was the Frenchman Mathieu Tillet, (17141791), the Royal Commissioner for Assays and Refining at the Paris Mint, who in 1779 published three articles about this method (23, 24, 25). In these he said that a good separation will always be achieved if the metals are properly alloyed (which can be obtained by cupellation), if the proportion of platinum is low (0.1 to 0.05 of the gold), if the proportion of silver is high (two or three times the amount of the remainder), and if the nitric acid used is not concentrated.

Although usually attributed to Tillet, this method of separation was certainly used in Spanish America at least fifty-six years earlier. It was described in a short report dated 15th June, 1726 and signed by Jos Sanchez de la Torre y Armas, who was the assayer at the Royal Mint in Santa F de Bogot, now known as Bogot (31).

I, Don Joseph Sanchez de la Torre y Armas, Assayer at the Real Casa de Monda give notice of the gold which was handed over to me on behalf of His Majesty by the Royal Officers of this Kingdom in six bars mixed with platina, which weighed five thousand nine hundred and fifty-eight castellanos for the purpose of separation, which was carried out using the following method.

He then goes on to describe briefly how the separation was performed. The method employed was based upon the fact that in practice gold is not alloyed with the naturally occurring platinum complex, which remains dispersed throughout the gold (5). The method consisted of two basic stages, the progress of which is shown in the Scheme.

Initial heating melted only the gold, because its melting point is substantially lower than that of platina. The platina-containing grains remained unaltered and, because their density is higher than that of gold, they sank to the bottom of the melting pot. Then decantation was used to separate the first portion of clean gold from the remainder. In this way the purified gold, amounting to about half the sample, was separated from the impure remainder (2900 castellanos), while 58 castellanos were lost during the process. The separation was not complete, however, because very small platinacontaining particles would have remained in suspension in the gold, while others, containing a high proportion of ruthenium, may also have been present in the molten material due to their low density (5).

The lower melting point and lower density of gold, compared with those of platina, formed the basis of a method of separation which according to this report dated 1766 was a usual method of separating these two materials

Consideration of the analysis shows that the composition of the clean gold separated out by this method was 18 carat. In the first place, this means that the original sample of impure gold containing platina was 18 carat, because only platina had been separated out during the fusion process due to its density. Secondly, it indicates that the 3000 catellanos were made up of 2250 castellanos of pure gold (24 carat) and 750 castellanos of perhaps silver or copper. We believe that this was most probably silver, because the next part of the procedure was generally used to separate gold from silver. So, melting could be considered as the third procedure for separating gold from platina. A report from the Viceroyalty of New Granada dated 1766 says:

The second stage of the separation concerned the 2900 castellanos of impure gold remaining behind after decantation, and which contained the platinum group metals. The original composition of this material would have been approximately 52 gold, 23 platinum and 25 per cent silver. Then the inquartation operation took place, involving the addition of silver in the ratio of 4:1. After melting and homogenisation the molten silver-rich alloy was poured into water, causing it to solidify as fine granules with a composition of 10 gold, 5 platina and 85 per cent silver.

These granules were then reacted with nitric acid which dissolved the silver and the platina, leaving the gold unaltered. The platinum group metals are not equally soluble, however, and probably only platinum and palladium would have dissolved in the acid, leaving ruthenium, rhodium, iridium and osmium undissolved; a more energetic action being required for their dissolution. However, when the composition of the ore from the Choc region is considered, see the Table, this degree of separation is quite acceptable.

As noted above, a sufficient addition of silver, proper homogenisation and a suitable concentration of nitric acid were required for this stage in the process to be carried out satisfactorily. Sanchez de la Torre noted:

Four and a half pounds of aqua fortis are needed to separate five marks as the process required repeated washing on account of resistance towards separation or towards absorbing other platina, causing a new alloy to form in some grains when the platina has amalgamated and does not contain sufficient silver for the aqua fortis to have effect.

One method could have been to precipitate silver and the platinum group metals together from solution using metallic copper. This was the system used to collect silver after it had been separated from gold in the beneficio de apartado (33). The mixture of silver and platinum group metals precipitated in this way could then be individually separated by treatment with nitric acid, after being melted and grained. This separation would be adequate, but not complete as some platinum and other elements would be dissolved in the nitric acid (34).

Another possibility could have been to separate the silver as silver chloride, and then to precipitate the platinum group metals with copper or another metal. This was the method used by Tillet many years later (24).

It is possible that the discovery of this inquartation method of platina separation could have been made by workers at the Royal Mint in Santa F. In any case the method was not well known; however, its origin can be found in the inquartation operation carried out to separate gold and silver by the apartado method. Ribaucourt said of inquartation:

The various methods I have mentioned for treating the alloy of these metals determine its proportions in the paste or mass which is to be separated. If the test shows that there is more or less than three times as much silver as gold in the mass, it is not suitable for the aqua fords separation process; but it is easy to add the necessary amount of silver to make it up to the appropriate proportions and this is how it is done. This stage is called inquartation since it reduces the ratio of gold in the total mass to a quarter.(35)

Several mistakes could possibly occur in the melting and inquartation methods of separation. If platina was alloyed with gold then it would not separate in the first beneficio by melting. Nevertheless only a very small amount would be involved, as there is little tendency for these elements to alloy. The same could happen with very fine grains of platina, which, as noted above, would not separate out by gravity but would be decanted in the clean gold.

We must also consider the fact that the dissolution of silver and platina by nitric acid is never complete. As has been said already, not all of the platinum group metals are soluble in nitric acid, indeed platina is not completely dissolved by this method either.

Tillet gave positive errors in the range of 0.3 to 1 per cent in the separation of platinum from the silver-gold-platinum alloy in which the platinum varied from 2.2 to 2.9 per cent (24). However, Vauquelin did not report errors if the platinum content was less than 5 per cent (30); interestingly, the proportion of platina in the inquartation alloy which was reported on by Sanchez de la Torre, was 5 per cent.

Using the costs given by Sanchez de la Torre it is calculated that the additional separation and purification processes required to remove the platina would increase the cost of gold by approximately 20 per cent (3 reales 12 maravedies is the cost of purification per castellano and 17 reales 4 maravedies the value of the gold purified). This, together with its illegal use to degrade gold, explains why platina was then regarded by the colonial authorities as a serious problem. Later of course the Spanish authorities made substantial amounts of metal freely available to European scientific institutions, so encouraging a continuing interest in the investigation and application of the properties of platinum and its allied metals.

The report by Sanchez de la Torre which has been examined here was also considered as part of the subject matter of an interesting earlier paper (36), the author of which drew somewhat different conclusions about the part that aqua fortis would have played in the separation process.

[1] The following units of mass were used in the original 18th century Spanish colonial documents. Conversion figures where known, are given (37). Pound = Peso = 460g, Mark = 230g, Castellano = 4.6g, Grano = 0.0648g.

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separation of silver from silver-manganese ore with cellulose as reductant - sciencedirect

separation of silver from silver-manganese ore with cellulose as reductant - sciencedirect

The silver in some silver-manganese ore with a grade of 3.15104 was concentrated by a combined beneficiation technique including magnetic separation, flotation, reducing leaching and gravity desliming. The major silver contained in manganese ore as isomorphism was concentrated by magnetic separation, while around 8.50% of the silver individual minerals were separated by flotation. The manganese in the mixed concentrate of both magnetic separation and flotation was dissolved in a reducing leaching, in which some cellulose reductant named CMK was used. Part of the slime contained in leach residue was removed by a laboratory desliming equipment. A silver concentrate with a grade of 4.96103 Ag and a recovery of 84.25% were obtained.

how is silver processed / made - extracted & purified

how is silver processed / made - extracted & purified

How is Silver processed Silver is most conductive and reflective metal on our earth. People have been making silver jewelry and other objects since about 4000 BC. Silver is not only used in jewelry. As 80% of silver is mined for industrial purposes. It is used mostly in electronic components and in construction as an insulation coating on glass. The mining company produces silver bars, composition of which is 93 97% pure silver. The company sells the bar to a refinery which further purify them for sale to industries.

Silver remains popular today because of its beauty and its affordability compared to gold and platinum. Pure silver is rather soft and its traditionally combined with one or more metals to give it strength and hardness. The silver used in the jewelry is sterling silver. As sterling is composed of 92.5% silver and 7.5% alloy. The alloy is usually copper or copper combined with other metals.

The action begins down in the mines where geologists point a light on gun at various spots in the rock face. The electronic device detects the level of 40 different elements including silver. The silver in its natural state isnt silver colored at all, rather than charcoal grey. Those silver looking deposits are actually zinc and lead. The miners drill holes in the silver rich areas where the geologists pin pointed. Then dynamite stick is inserted for the blast into the rock. After the blast carts hold the chunks of rock called ore to the surface. Geologist then test ore piles and blend them as required, as to achieve a consistent amount of silver content per Kg of ore.

The silver processed took some time. The ore first goes into the primary crusher. The machines huge steel teeth break up the big chunks into smaller pieces. Then those pieces drop through grades below into the secondary crusher which breaks them down into smaller pieces. Then these pieces goes into a vibrating cone crushers which pulverize them into tiny pieces.

A conveyor then transports the crushed ore to the ball mill. At this point the ore pieces are roughly 6 mm big. As the mills large cylinder rotates, steel balls bounce around inside grinding the ore into powder. Then a water circulation system flushes the silver rich powder out of the cylinder into the large tanks which keeps the water moving. As to separate and dissolve the metals that powder contains, the worker pour in acid. After 72 hours, the rock waste settled at the bottom.

The solution containing dissolved silver is pumped through filter presses. The filter plate are treated with a zinc based chemical which attracts silver molecules. As the solution passes through, the plates trap particles containing silver forming a layer of black powder called silver precipitate. This precipitate is composed of approximately 50% of silver and 50% waste. As the waste being a jumbled of various metals dirt and other type of impurities. To separate the silver from the waste, they first dry the precipitate in a gas furnace for a couple of hours.

In the lab of mining companies, technicians continuously ore samples to determine the grade. The term for the quantity of silver per Kg of ore. Then the workers heat the samples to 1093 degrees Celsius for about an hour to burn off the impurities. As after the burn off, the silver and other metals are left like Lead, Copper, Zinc, Cadmium and Selenium. Then the lab technicians treat the samples with the chemical that prevents silver from burning off and then put them back in the oven. Now when the samples comes out about an hour later, all the other metals have burnt off and only silver is left behind.

The workers then weight the silver and compares it to the weight of the original sample in order to calculate the grade. As the key to running the profitable mind is ti ensure that the grade is consistently with in certain parameters. The workers put the now dried silver precipitate into an oven along with chemicals which prevents silver from burning off. 4 hours later, the silver and waste have separated and melted. Then the workers pour them into bar shaped molds. The silver being heavier settles at the bottom. Finally the workers skim off the waste floating on top. In less than 5 minutes, the molten silver cool and hardens, enabling workers to extract what is now a silver bar. Then the mining company sells the bar to a refinery for processing into industrial grade silver.

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