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Gold parting

Gold parting is a metallurgical process employed to separate gold from silver and other base metals in alloys, enabling the production of high-purity gold essential for coinage, jewelry, and industrial uses.^[1]^[2] This selective corrosion technique exploits gold's resistance to certain chemicals while dissolving the accompanying metals, typically achieving gold purities of 994 to 999 fine.^[2] Historically, gold parting originated with the salt cementation method in ancient Lydia around the 6th century BCE, during the reign of King Croesus, where electrum (a natural gold-silver alloy) was heated with sodium chloride at approximately 800°C to volatilize silver as chloride compounds, leaving purified gold behind.^[3] Evidence suggests even earlier applications, potentially as far back as 1900 BCE in the Middle Kingdom of Egypt, based on artifacts like the Tod Treasure.^[3] This innovation facilitated the minting of standardized pure gold currency and spread to regions such as Mesopotamia, Elam, and Achaemenid Persia.^[3] In modern practice, nitric acid parting has largely supplanted earlier techniques, involving the granulation or rolling of alloys followed by immersion in dilute nitric acid solutions of varying strengths (specific gravities 1.2 to 1.3) to dissolve silver into silver nitrate, with residual gold collected after boiling, decanting, and washing.^[1]^[2] The process, scalable for industrial refining of bullion or precise laboratory assays, minimizes gold loss to 0.01–0.03% while retaining trace silver (0.05–0.1%) in the final product, often requiring corrections for accuracy in mint operations.^[1] Although effective, it generates nitrogen oxide emissions necessitating environmental controls, and alternatives like the Miller chlorination process are sometimes preferred for large-scale operations.^[2]

Fundamentals

Definition and Purpose

Gold parting is a metallurgical process that selectively separates gold from silver and base metals in alloys, enabling the production of higher-purity gold materials.^[4] This separation is essential because gold and silver are frequently co-extracted from ores and form stable alloys, necessitating targeted chemical or electrochemical methods to isolate the noble metal.^[4] Historically, gold parting addressed the limitations of natural electrum, a gold-silver alloy typically containing 20–80% gold along with varying amounts of silver and trace elements like copper.^[5]^[6] Electrum served as the primary starting material in ancient refining, where its variable composition made consistent purity challenging without parting techniques.^[5] The primary purposes of gold parting include enhancing the economic value of gold by increasing its purity for applications in coinage, jewelry, and industrial uses, as well as standardizing metal content for reliable trade and monetary systems—such as producing nearly pure gold coins from alloyed bullion.^[7] It also prepares separated gold for further refining steps, ensuring compliance with purity standards that boost marketability and usability.^[8] A key challenge in gold parting arises from the chemical similarity between gold and silver, particularly their shared nobility, which complicates separation and requires methods exploiting subtle differences like the inertness of gold versus the reactivity of silver to specific reagents.^[9]^[2]

Chemical Principles

Gold parting relies on the pronounced chemical nobility of gold, which exhibits exceptional resistance to oxidation and dissolution in most acids due to its high standard electrode potential of E^\circ (Au^{3+}/Au) = +1.50 V.^[10] This nobility stems from gold's position as a late transition metal, making the reduction of Au³⁺ to metallic gold highly favorable compared to common oxidizing agents like nitric acid or sulfuric acid. Only aqua regia, a mixture of concentrated nitric and hydrochloric acids, can dissolve gold by forming stable chloroauric acid complexes (HAuCl₄).^[11] In contrast, silver, often alloyed with gold, is far more reactive, with a lower standard electrode potential of E^\circ (Ag^{+}/Ag) = +0.80 V, allowing it to be selectively oxidized and dissolved under acidic conditions.^[12] The reactivity of silver enables its conversion to highly soluble silver nitrate (AgNO₃) in nitric acid, with a solubility of approximately 2150 g/L at 20°C, facilitating efficient separation from gold.^[13] In chloride-based environments, silver forms silver chloride (AgCl), which is sparingly soluble (Ksp ≈ 1.8 × 10⁻¹⁰), precipitating as a solid to aid parting.^[14] These solubility differences underpin the selective extraction of silver from gold-silver alloys, where the alloy's microstructure allows acid penetration to target silver atoms while leaving gold intact. A key reaction in nitric acid-based parting is the oxidation of silver:

$3Ag + 4HNO_3 \rightarrow 3AgNO_3 + NO + 2H_2O

This redox process involves nitrate ions acting as oxidants, producing soluble AgNO₃ and nitrogen monoxide gas, while gold remains undissolved due to its inertness toward nitric acid.^[13]^[15] To ensure complete silver removal without excessive acid consumption or gold loss, inquartation dilutes the gold content to approximately 25% by adding silver, achieving a 3:1 Ag:Au ratio that maximizes surface area exposure and promotes uniform dealloying.^[15] Common impurities such as base metals like copper are preferentially dissolved in nitric acid during parting, as copper readily forms soluble copper(II) nitrate (Cu(NO₃)₂) via oxidation, further purifying the residual gold.^[16] This selective dissolution exploits the lower nobility of base metals (e.g., E^\circ (Cu^{2+}/Cu) = +0.34 V), ensuring they do not contaminate the parted gold.^[12]

Historical Development

Ancient and Early Techniques

The earliest known techniques for gold parting emerged in the prehistoric Near East during the Chalcolithic period, around the 4th millennium BC, where depletion gilding was employed to remove silver from the surface of electrum alloys through oxidation. This method involved heating gold-silver alloys to form a silver oxide layer on the surface, which was then mechanically removed by abrasion or chemical means, leaving a thin layer of nearly pure gold. Archaeological evidence from Nahal Qanah Cave in Israel includes gold rings and circlets dated to approximately 4000–3500 BC, analyzed as electrum objects that exhibit signs of surface enrichment consistent with depletion gilding, marking the initial experimentation with separating precious metals in the southern Levant.^[17]^[18] Recent analysis of artifacts from the Tod Treasure, discovered at the Temple of Montu in El-Tod, Egypt, provides evidence of salt cementation gold parting as early as the Middle Kingdom (circa 1900 BCE, during the reign of Amenemhat II). Isotopic studies of silver objects indicate that the silver was likely separated from gold via heating with salt, volatilizing silver chloride and leaving purified gold, predating similar techniques elsewhere.^[3] By the Early Bronze Age, in the 3rd millennium BC, Mesopotamian artisans at Ur developed mercury gilding, also known as fire gilding, as a related but distinct surface treatment for applying gold to base metals or enhancing alloys, though it did not achieve true bulk parting of gold from silver. This process entailed amalgamating gold with mercury to form a paste applied to objects, followed by heating to evaporate the mercury and deposit a gold layer, as evidenced by artifacts from the Royal Tombs of Ur, including gilded items showing mercury residues. While innovative for decorative purposes, mercury gilding primarily coated surfaces rather than separating metals throughout the material, limiting its role in refining electrum ores.^[19] A significant advancement occurred in the 6th century BC in Lydia, at Sardis, where salt cementation was introduced as an early documented method for bulk separation of gold from silver in electrum. Electrum was hammered into thin sheets or granules and layered with salt—likely rock salt—in coarse pottery crucibles, then heated in brick ovens to around 800°C, allowing chlorine gas from the salt to react preferentially with silver, forming soluble silver chloride that was absorbed by the porous vessel walls, leaving behind purified gold. Archaeological excavations at Sector PN near the Pactolus River uncovered crucibles with residual gold, salt traces, and furnace structures dated to the mid-6th century BC, confirming this as a verified industrial-scale parting technique in the ancient world.^[20] In ancient India, the Arthashastra, attributed to Kautilya and dated to the 4th century BC, describes a salt-based separation process for purifying gold dust, emphasizing the use of thin sheets of impure gold treated with salt to facilitate the removal of base metals through heating. This method involved mixing gold dust with salt and other fluxes before melting, leveraging the chemical difference where silver and impurities form chlorides more readily than gold, allowing for their extraction and yielding higher-purity gold suitable for coinage and ornaments. The text underscores quality control, such as using touchstones to verify purity post-treatment, reflecting systematic state oversight of metallurgical practices.^[21] These ancient and early techniques were inherently limited by their low efficiency, often affecting merely the surface layers rather than the entire volume of material, which restricted their application to small-scale or decorative refining without enabling large-volume production of high-purity bullion.^[20]

Medieval and Post-Medieval Advances

In the 12th century, Theophilus Presbyter documented one of the earliest detailed European descriptions of the salt cementation process for gold parting in his treatise De diversis artibus. He instructed the use of brick dust moistened with urine and mixed with rock or sea salt in a 2:1 mass ratio to form a cement, into which thin gold foils were embedded alternately without touching one another, then sealed in a ceramic vessel and heated in a furnace for at least one night. This method, building on ancient precursors like those from Lydia, selectively removed silver and base metals as chlorides while leaving purified gold behind, achieving silver contents below 2% in the residue.^[7] During the Islamic Golden Age, alchemists such as Jābir ibn Ḥayyān advanced knowledge of acids critical to refining, including the development of aqua regia—a mixture of nitric and hydrochloric acids capable of dissolving gold—with the first clear descriptions of nitric acid appearing in the 13th century through distillation of saltpeter with vitriol. These innovations facilitated more effective separation techniques and likely influenced European practices via translations of Arabic texts. By the 13th century, these ideas transmitted to Europe, where nitric acid parting emerged around 1300–1400, allowing for bulk separation of gold from silver alloys by dissolving the silver without attacking the gold. Albertus Magnus provided the first clear European mention of nitric acid for this purpose in the 13th century, marking a shift from labor-intensive cementation to more efficient chemical dissolution.^[22]^[4] By the 16th century, assay manuals like the Probierbüchlein, an early German text on precious metal testing, outlined sulfur and antimony methods that formed silver sulfide to isolate gold from alloys. These involved heating impure gold with elemental sulfur or antimony under controlled conditions in sealed crucibles, volatilizing impurities while enriching the gold residue, and represented a refinement of earlier sulfide-based separations for assay and small-scale refining. Post-medieval advancements culminated in the widespread adoption of acid-based parting at major mints, such as the Venetian Mint around 1475 and various German facilities by the early 1500s, where nitric acid enabled industrial-scale coin refining and ensured high-purity gold for currency production.^[23]

19th-Century Innovations

The California and Australian gold rushes of the mid-19th century generated vast quantities of gold ore often heavily alloyed with silver and other impurities, creating an urgent demand for scalable refining techniques to process large volumes efficiently.^[24] These events, peaking around 1849 in California and 1851 in Victoria, Australia, shifted gold parting from artisanal methods to industrial practices, as traditional processes proved inadequate for the influx of low-grade bullion.^[24] In the 1860s, the Miller process emerged in Australia as a breakthrough for large-scale silver removal, involving the introduction of chlorine gas into molten impure gold to form silver chloride, which could be skimmed off.^[25] Patented in 1867 by Francis Bowyer Miller, this method allowed refiners to handle thousands of ounces daily, producing gold of approximately 99.5% purity suitable for bullion production.^[26] Concurrently, sulfuric acid gained traction as a cost-effective alternative to nitric acid for parting in flasks or crucibles, particularly for silver-rich alloys, by heating the mixture to drive off silver sulfate while leaving gold intact.^[27] By 1874, Emil Wohlwill in Hamburg, Germany, invented the electrolytic Wohlwill process, which further elevated purity levels to 99.99% through anode dissolution of impure gold in a chloride electrolyte, depositing pure gold on the cathode.^[28] This innovation addressed limitations in chemical methods by enabling precise control over impurities like platinum group metals.^[29] These 19th-century advancements collectively facilitated gold purities exceeding 99%, underpinning the global adoption of the gold standard from the 1870s onward by ensuring consistent, verifiable quality for international trade and coinage.^[30] The transition to factory-scale operations during this era transformed gold parting into a cornerstone of modern metallurgy, supporting economic stability amid expanding mining outputs.^[25]

Traditional Processes

Salt Cementation

Salt cementation, a pyrometallurgical technique for separating gold from silver in alloys, served as the predominant non-acidic method from the 6th century BC until the 16th century AD, with early adoption in ancient Lydia for refining electrum.^[7] This process was especially suited to low-silver alloys containing less than 20% silver, where it efficiently removed the base metal while preserving gold integrity.^[31] The procedure begins by preparing the gold-silver alloy in thin foils or powder form, which is then intimately mixed with common salt (NaCl), powdered burnt clay or brick dust as a binder, and occasionally urine or other organic matter to achieve a pasty consistency for even distribution.^[32] This mixture is layered into a clay-sealed ceramic crucible or vessel to prevent gas escape, then heated in a furnace to 600–900°C, allowing thermal decomposition and reaction to proceed.^[7] At these temperatures, the salt interacts with oxygen and silicates from the clay, generating chlorine gas or hydrochloric acid that selectively attacks silver.^[32] The core chemical reaction involves the formation of volatile silver chloride: Cl₂ + 2Ag → 2AgCl, where silver chloride sublimes and escapes as vapor, while gold remains unmelted and unaffected due to its higher melting point and chemical inertness.^[32] Impurities such as base metals form slag with the clay and are skimmed off or left behind, purifying the residual gold button.^[31] The process duration varies from several hours for initial parting to multiple days for iterative cycles, often requiring 19–20 hours per heating stage and repetition to reduce silver below 0.3%.^[32] This method's advantages lie in its rudimentary requirements—no strong acids or complex equipment needed—enabling widespread use in pre-industrial settings for achieving gold purities up to 99.7%.^[32] It effectively removed silver that cupellation alone could not, enhancing alloy quality for coinage and artifacts.^[31] However, drawbacks include labor-intensive preparation and firing, inefficiency with high-silver alloys (>20% Ag) due to slower diffusion and incomplete reaction, and potential gold losses of up to 5% from adhesion to crucible walls or volatilization.^[7]

Sulfur and Antimony Methods

The sulfur and antimony methods for gold parting involve thermal processes that exploit the formation of insoluble silver sulfide to separate silver from gold-silver alloys, primarily used in historical assaying and refining. These techniques, documented in medieval and early modern European texts, apply sulfur or antimony trisulfide (Sb₂S₃, also known as stibnite) to powdered alloys, offering a faster alternative to salt-based cementation by promoting sulfide reactions in a controlled heating environment.^[33]^[34] In the procedure, the gold-silver alloy is first powdered and intimately mixed with elemental sulfur or antimony trisulfide in a suitable crucible or mold, such as a conical fusorius made of clay or metal. The mixture is then heated to temperatures between 500°C and 700°C in a small furnace, allowing sulfur to react selectively with silver while gold remains largely unaffected and collects at the bottom or center. Antimony trisulfide serves as both a sulfur source and a carrier, facilitating the transport of sulfur to the silver particles and forming a slag-like layer of silver sulfide (Ag₂S) that can be mechanically separated; any antimony that alloys with the gold is later removed by oxidation or volatilization. The key reaction is $2Ag + S \rightarrow Ag_2S, which occurs preferentially due to silver's higher affinity for sulfur compared to gold.^[4]^[33] These methods trace their origins to medieval practices, with sulfur-based parting first described by Theophilus Presbyter in the 12th century, and antimony variants detailed in 16th-century German texts such as the Probierbüchlein, where they were employed for assaying ores and refining bullion in mining regions like Saxony. Building on earlier medieval documentation of sulfide uses in metallurgy, the processes were valued for their speed over salt cementation, completing separation in a single heating cycle rather than requiring prolonged exposure, though they carried higher risks due to volatile compounds.^[34]^[33] Efficiency in these methods typically achieves approximately 95% gold purity in one pass, with experimental recreations showing near-complete silver removal (up to 99% in optimized conditions) and reduced losses from gold encapsulation compared to purely sulfur-based approaches, as antimony helps fluidize the mixture. The antimony variant minimizes gold entrapment in the sulfide slag by alloying temporarily with gold, allowing cleaner separation upon subsequent treatment.^[4]^[33] Despite their effectiveness, the sulfur and antimony methods have notable drawbacks, including the release of toxic fumes from antimony trisulfide volatilization, which posed health risks to operators, and potential contamination of the gold with antimony residues that could require additional refining steps like air oxidation to achieve higher purity. These thermal, dry processes contrasted with liquid-based alternatives by avoiding acids but were eventually supplanted by safer electrolytic methods in the 19th century.^[4]^[34]

Nitric Acid Parting

Nitric acid parting is a selective dissolution process used to separate gold from silver in alloys, relying on the chemical inertness of gold to nitric acid while silver readily forms soluble silver nitrate. This method, particularly effective for alloys with high silver content, involves first diluting the gold through inquartation to ensure complete silver removal without significant gold loss.^[2] The process produces a porous gold residue that can be further refined, making it suitable for laboratory-scale or small-batch operations.^[35] The inquartation step begins by alloying the gold-containing material with silver to achieve approximately a 25% gold content by weight, typically in a 3:1 silver-to-gold ratio, which prevents excessive gold dissolution during acid treatment. This dilution is accomplished by melting the gold with silver (or sometimes copper as a substitute base metal) and casting the alloy into a homogeneous form. Granulation follows, where the alloy is poured into water to create small, high-surface-area particles that enhance the efficiency of the subsequent acid attack.^[36]^[37]^[35] In the procedural steps, the granulated alloy is boiled in dilute nitric acid, typically 20-50% concentration (such as 5.6 M initially), for about 30 minutes to several hours to dissolve the silver as silver nitrate, leaving behind a brown, spongy gold residue. The mixture is then filtered to separate the gold, which is washed with water and additional dilute acid to remove residual silver. This is repeated with stronger nitric acid (up to 9.4 M or 68% concentration) to ensure thorough silver removal, followed by final washing and drying of the gold residue. Silver is recovered from the nitrate solution through precipitation methods, such as adding copper to displace silver or using caustic soda for further processing.^[36]^[2]^[37] The key reaction involves the oxidation of silver by nitric acid (for dilute conditions), represented as:

$3 \mathrm{Ag} + 4 \mathrm{HNO_3} \rightarrow 3 \mathrm{AgNO_3} + \mathrm{NO} + 2 \mathrm{H_2O}

Gold remains completely inert to nitric acid under these conditions. The inquartation ensures that the silver is fully accessible to the acid; if the initial gold content exceeds approximately 25-30%, some silver may remain undissolved, trapped within the resulting gold structure.^[36]^[35]^[2] This technique originated in 13th-century Europe following the discovery of nitric acid by alchemists, who adapted it from earlier selective corrosion methods, and it became a standard for small-scale refining in 19th-century laboratories due to its simplicity and effectiveness for batch processing.^[2]^[35] Yields typically exceed 99%, with the resulting gold achieving purities of 99-99.9% (994-999 fine), depending on the number of acid treatments and alloy composition.^[37]^[36]^[2]

Modern Methods

Miller Process

The Miller process, a pyrometallurgical method for refining gold, was invented in the 1860s by Francis Bowyer Miller, an assayer who worked at the Sydney Branch of the Royal Mint in Australia, and patented in Britain in 1867.^[25]^[38] First implemented at the Sydney Mint and later at the Auckland Mint by 1869, it became a cornerstone of industrial gold refining due to its efficiency in handling large volumes of impure gold-silver alloys, known as doré bars.^[25] In the procedure, impure doré is melted in a furnace at temperatures of 1000–1100°C, typically covered with a flux layer of borax and silica to protect the melt and facilitate slag formation.^[38] Chlorine gas is then introduced and bubbled through or passed over the molten alloy, selectively reacting with silver and other base metal impurities such as copper, lead, iron, and zinc to form volatile or solid chlorides.^[38] These chlorides rise to the surface as a skim or are carried off in exhaust gases, allowing them to be removed periodically; the process concludes when the exiting chlorine fumes exhibit a characteristic color change upon condensation on a cold surface, indicating near-complete reaction.^[38] The primary reaction for silver removal is $2Ag + Cl_2 \rightarrow 2AgCl, where gold remains in the molten state unaffected due to the instability of gold chloride at these temperatures.^[38] The resulting gold achieves a purity of approximately 99.5% (995 fineness), with residual impurities primarily consisting of minor silver and copper.^[39] Silver and other metals are recovered from the chloride slag through subsequent treatments, such as dissolution in sodium carbonate solutions, minimizing losses to about 1–2% of the gold content entrained in the slag.^[38] This method's advantages include rapid processing times—typically completing in a few hours—and scalability for refining tons of material at low cost, making it suitable for large-scale refinery operations worldwide.^[25]^[38] However, it presents disadvantages such as the hazards associated with handling toxic chlorine gas and the production of corrosive byproducts, alongside its limitation to moderate purity levels compared to electrolytic alternatives.^[38] By the mid-1990s, estimates indicated that two-thirds of globally refined gold utilized this process.^[25]

Wohlwill Process

The Wohlwill process is an electrolytic refining technique designed to achieve investment-grade purity in gold, typically starting from impure gold anodes produced by prior methods such as the Miller process. Patented in 1874 by German engineer Emil Wohlwill, the process involves the electrochemical separation of gold from impurities like silver and base metals, resulting in cathode deposits of exceptionally pure gold. It has been adopted by major industrial refineries, including Rand Refinery in South Africa, for producing high-purity bullion suitable for investment and fabrication.^[40]^[29]^[41] The setup consists of an electrolytic cell with an anode cast from impure gold (typically 90-98% pure), a cathode in the form of a thin starter sheet of pure gold, and an electrolyte solution of gold chloride (AuCl₃) dissolved in hydrochloric acid (HCl), approximately 120 g/L gold with 5–10% free HCl. The impure gold anode, often sourced from Miller process output containing residual silver and base metals, serves as the source material for dissolution.^[42]^[43] In the procedure, direct current electrolysis is applied at a low voltage of 3-4 V and a temperature maintained between 60-80°C to optimize gold solubility and deposition rates. Gold ions dissolve from the anode and migrate to the cathode, where they deposit as pure metal, while silver precipitates primarily as silver chloride sludge and base metals either dissolve into the electrolyte or form insoluble residues. The process operates continuously, with anodes typically lasting 16-18 hours before replacement, and the electrolyte is circulated to prevent buildup of impurities.^[43]^[42]^[44] The key cathodic reaction is the reduction of gold tetrachloroaurate ions:

\ce{AuCl4^- + 3e^- -> Au + 4Cl^-}

At the anode, gold oxidizes to Au³⁺ ions, which complex with chloride to form the soluble AuCl₄⁻ species.^[42] The output is gold of 99.99% or greater purity, often reaching 99.999% in optimized operations, with overall recovery efficiency around 95% due to minimal losses in the slime and electrolyte. The anode slime, a byproduct rich in platinum group metals (PGMs) such as platinum and palladium, is collected and further processed for valuable recoveries. Energy consumption for the electrolysis is approximately 3-5 kWh per kg of gold refined, reflecting the low-voltage, high-amperage conditions.^[42]^[45]^[46]

Acid-Less Separation

Acidless separation, also known as Acidless Separation (ALS), is a modern vacuum distillation technique designed as an environmentally friendly alternative to traditional acid-based methods for separating gold from high-silver alloys, particularly those containing over 50% silver such as jewelry scrap.^[47] Developed through a collaboration between the Italian firm IKOI Srl and Russia's Ekaterinburg Non-Ferrous Metals Processing Plant (EZ-OCM), the process was refined and patented around 2014, with commercial adoption beginning by 2016 among LBMA-accredited refineries.^[48] Unlike historical nitric acid parting, which relies on chemical dissolution and generates hazardous waste, ALS employs thermal evaporation without any acids or chemicals, achieving zero emissions and simplifying waste management.^[49] The procedure involves placing the alloy in a vacuum chamber and heating it to temperatures between 1300°C and 1450°C under a high vacuum of 10^{-2} to 10^{-3} mbar (approximately 7.5 \times 10^{-3} to 10^{-3} torr), where silver and other volatile elements like zinc volatilize as vapors while gold remains as a solid residue.^[47] These vapors are then condensed on a cooled surface, allowing for selective separation based on differences in vapor pressures; for instance, silver, which boils at 2162°C under atmospheric conditions, evaporates at significantly lower temperatures under vacuum due to reduced pressure.^[48] The process is fully automated, typically handling batches of 15–200 kg depending on system configuration, and results in gold of 99.9% purity suitable for further refining, with no metal losses reported.^[50]^[51] Key advantages include the elimination of chemical reagents, which avoids the production of NOx emissions and acidic effluents associated with traditional wet methods, making it ideal for sustainable operations in compliance with ESG standards.^[49] Refineries such as ABC Refinery in Australia and MMTC-PAMP in India have integrated ALS into their workflows by 2019, leveraging its cost-effectiveness and versatility for alloys with varying compositions.^[50] As of 2025, the technology continues to see growing adoption in global precious metals refining, particularly for processing dore and scrap with high silver content, driven by increasing regulatory pressures on environmental impacts; adoption has expanded to include The Perth Mint in Australia.^[47]^[52]

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Leyden Papyrus has a recipe for colouring gold which is, in reality, a method of parting gold and ... gold coinage of Edward III around 1350 (35). These ...
[33]
Gold Parting using Nitric Acid - 911Metallurgist
Mar 24, 2016 · The ideal gold leaching formula is 7:1 (7 parts brine water to 1 part nitric acid), at a leaching temperature between, a low of 70 F and a maximum of 176 F.
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Inquartation and Parting Refining Process - Ganoksin
Sep 29, 2016 · The acid treatment is known as parting as it 'parts' (separates) the gold from the silver and base metals. Dilution of the gold content is ...<|control11|><|separator|>
[35]
US4857107A - Gold inquartation process - Google Patents
A method of refining a precious metal comprising the steps of inquarting the material containing the precious metal into an alloy.
[36]
Gold Chlorination Process by Miller - 911Metallurgist
Jul 8, 2015 · Miller's Gold Chlorination process was introduced by F.B. Miller. The refining process employs chlorine gas, which passed into molten gold ...<|separator|>
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[PDF] Flow Studies for Recycling Metal Commodities in the United States
gold bullion made by the Miller process is 996 to 997 fine. A3. (99.6 to 99.7 ... A petroleum-refining process that uses a platinum catalyst to convert ...
[38]
Electrorefining in Sustainable Metals Production - MDPI
The Wohlwill process to refine gold was invented in 1874 and the Moebius process to refine silver in 1884. The aim of these processes was to produce more ...Missing: Emil | Show results with:Emil
[39]
Gold production at the Rand Refinery
gold, the Rand Refinery is now also in a position to supply this need. This new section employs the. Wohlwill process for refining gold by electrolysis.
[40]
[PDF] Refining Precious Metal Wastes - rexresearch1
The advantages and disadvantages of the two methods will be discussed in Chapter XX. In general wash-barrel residues are handled nearly the same as floor ...
[41]
Purification of Gold by Electrolysis - 911Metallurgist
Nov 4, 2016 · The liquid is heated from 60° to 70° C. If the temperature is allowed to fall, or the acid is omitted, chlorine escapes. The cathode consists of ...
[42]
Wohlwill electrolytic refining process for gold - Finishing.com
... voltage of 2.5 to 3 volts depending on your local Temperature .The cell ideally should be Maintained at 22 to 25 °C.Thanks I hope it helps you. and now ...
[43]
[PDF] Extraction and Recovery of Gold from both Primary and Secondary ...
Very high-grade gold (99.99% purity) can also be acquired by electrolytic refining methods. The Wohlwill process is a well-known refining method in which tiny ...Missing: setup output
[44]
Process technology development at Rand Refinery - ResearchGate
Aug 6, 2025 · ... The electrorefining of gold is usually achieved by wellknown Wohlwill process that involves dissolution of gold from a gold scrap in a ...Missing: voltage | Show results with:voltage
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[PDF] Evolution of ALS Technology - India Gold Conference
Aug 4, 2023 · ALS is a pre-refining process to remove silver from. Au/Ag/Cu alloys using vacuum distillation technology.Missing: parting | Show results with:parting
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Acidless Separation | Alchemist - LBMA
Acidless Separation (ALS) is a 'green' refining process developed by IKOI and EZ-OCM for precious metal refiners.Missing: parting | Show results with:parting
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Reduced environmental impacts for the precious metal refining ...
Apr 1, 2021 · The original AcidLess technology, developed by IKOI, separates gold from precious metal alloys using differential evaporation and condensation ...Missing: parting | Show results with:parting
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ABC Refinery Utilises Acidless Separation Technology
Acidless Separation (ALS) removes silver and light elements from alloys using vacuum distillation, with no chemicals, fumes, or smoke, and separates gold and ...