Abstract: A method is shown for raising the pH of a cyanide leach solution of the type used in a heap leaching mining operation. Lime slurry is mixed with a side stream of barren cyanide solution in a reactor vessel in order to remove carbonate hardness, to regenerate the hydroxide alkalinity and to raise the pH of the resulting recausticized leach solution. A portion of the calcium carbonate precipitate formed in the reactor vessel is retained in order to encourage further crystal growth. Overflow from the reactor vessel passes through one or more cyclone separation stages in order to remove particulate solids. A cyclone overflow stream is directed back to the process to upwardly adjust the pH of the bulk of the barren cyanide solution. A cyclone underflow stream is directed back to the reactor vessel to provide seed crystal nuclei for precipitate growth.

Abstract: A method for extraction a metal from a mineral ore including a refractory ore contained in a metal. The method includes concentration of refractory ore followed by micronization of the concentrate until gold is liberated by the extraction solution and mixing of micronized concentrate with concentration rejects or by-products to facilitate recovery of the treatment solution.

Abstract: Precious metals such as gold can be extracted from a refractory ore using a conventional cyanide leaching step and with reduced cyanide consumption by pre-treating the ore prior to cyanide leaching. The refractory ore is pretreated by fine grinding and an initial leaching step which uses inexpensive limestone and lime to maintain the initial leach relatively alkaline. Oxygen is added to the initial leaching step and the conditions are carefully controlled to only partially oxidize the ground ore to between 9-15%. The initial leaching step can be carried out at temperatures of less than 100 degrees C. and at atmospheric pressures. The pre-treated ore is then leached by a conventional cyanide leaching step to recover the precious metal and cyanide consumption can be reduced by more than two thirds.

Abstract: A method is provided by which rice hull ash is pelletized for use in steelmaking The rice hull ash is blended with lime or dolime, and also with a mixture of water and molasses. This generates heat as the lime and water react to form lime hydroxide, a known binder. The heat thus generated reduces the energy required for drying the pellets.

Abstract: In one aspect, the present invention provides a method for recovering precious metal, and particularly gold, from a particulate substrate loaded with a precious metal-containing coating, in which a portion, but less than substantially all, of the particulate substrate is dissolved away to physically release precious metal-containing coating from the particulate substrate. The particulate substrate loaded with a precious metal-containing coating may be prepared during precious metal recovery operations by cementation of precious metal on a base metal particulate substrate from a pregnant leach solution, such as a leach solution including a thiosulfate lixiviant for the precious metal.

Abstract: Recovery of gold from alkaline cyanide leach solutions using ion exchange adsorbents, comprising (a) contacting the cyanide leach solution containing the gold with an extraction reagent comprised of a solid adsorbent carrying an organic base functionality of a compound having a pK.sub.a between about 9-14, such as a guanidyl functionality, to adsorb gold and eluting the adsorbed gold from the solid adsorbent with an aqueous alkaline eluant solution having a pH above about 12 and containing an alkali metal salt of an aromatic or aliphatic carboxylic acid having from about 4-14 carbon atoms, the eluant solution having incorprated therein from about 0.001 moles to about 0.2 moles per liter of an alkali metal cyanide salt. The solid adsorbent containing the aurocyanide complex may be contacted with a concentrated aqueous solution of a zinc tetracyanide salt whereby the aurocyanide complex is displaced with a zinc tetracyanide complex before treatment with the eluant solution.

Abstract: A powerful reducing agent such as hydrazine monohydrate is added to the standard eluent solutions such as NsOH-NaCN with or without alcohol. The kinetics of elution of gold or of silver are thus markedly enhanced.

Abstract: A hydrometallurgical process for treating copper feed materials containing gold and/or silver by simultaneously leaching copper, gold and/or silver into an aqueous cyanide solution, recovering copper in metallic form by electrowinning and regenerating cyanide ions is provided, wherein high current efficiencies are achieved at high current densities and at low copper concentrations.

Abstract: A pulp with ph=9.5 to 11.5, resin, and cyanide KCN is fed to a reaction zone. KCN is in a concentration of CN.sup.- ions in the liquid phase of the pulp from about 0.1 to about 10 g/l, which is maintained constant. The sorbent is in an amount providing its concentration 1 to 1.5% of the reaction zone volume. The leaching procedure produces a sorbent with impurities and rich in gold and silver, and a cyanic pulp depleted of gold and silver. Then, the sorbent rich in gold and silver is separated from the cyanic pulp. The saturated sorbent with impurities is processed in the desorption zone in two stages by passing therethrough a sulfuric acid solution of thiourea, the volume of the solution comprising 10 to 15 volumes of said sorbent. The sulfuric acid solution of thiourea is in an amount of 30% to 50% of said solution volume. A sulfuric acid solution of thiourea rich in gold and silver and a sorbent depleted of gold, silver and impurities is obtained.

Abstract: A hydrometallurgical process for treating copper ores or concentrates containing gold by simultaneously leaching both copper and gold into an aqueous cyanide solution, recovering copper and gold in metallic form by electrowinning or cementation and regenerating cyanide ions is provided.

Abstract: A process for recovering at least one precious metal from an ore containing carbonaceous material is disclosed. The process involves the use of certain plant derived ortho-quinone containing components, in particular, certain lignin and/or tannin derived components containing ortho-quinone functionality.Preferred compositions comprise at least one ligno sulfonate component containing ortho-quinone functionality. In the process, the use of at least one additional oxidant capable of maintaining the ortho-quinone containing functionality in the desired oxidation state provides for integrated process synergy.

Abstract: A process for recovering at least one precious metal from an ore containing metal sulfide material is disclosed. The process involves the use of promoting amounts of certain plant derived ortho-quinone containing components, in particular, certain lignin and/or tannin derived components containing ortho-quinone functionality. Preferred compositions comprise at least one ligno sulfonate component containing ortho-quinone functionality. In the process, the use of at least one additional oxidant capable of maintaining the ortho-quinone containing functionality in the desired oxidation state provides for integrated process synergy.

Abstract: A method of recovering precious metals from a silver bearing ore containing polybasite, pearcite, pyrargyrite, tetrahedrite or argentite by mixing the ore with an alkali metal or alkaline earth metal peroxide in slurry or solid, leaching the ore with a cyanide solution, and recovering the precious metals from the cyanide solution.

Abstract: A process for recycling hydrogen cyanide from a cyanide-containing slurry is provided. The process includes the steps of adjusting the pH of a cyanide-containing slurry, volatilizing HCN contained in the pH adjusted slurry and contacting the volatilized HCN with a precious metals-containing slurry to recover precious metals therefrom. Alternatively, the HCN can be contacted with reclaim, or decant, water to recover cyanide, thereby conserving resources.

Abstract: A method for improving the yield of gold and silver from a Merrill-Crowe recovery process where the presence of copper effects yield. The method involves the addition of a substoichiometric amount of ethylenediaminetetraacetic acid in combination with a phosphonate and polyacrylic copolymer scale control agent. The method also reduces zinc consumption and controls scaling in the stripping circuit.

Abstract: Mill tailings containing cyanide species can be treated with carbon dioxide in order to drive-off and/or recover the cyanide content of said tailings.

Abstract: A process for removing and recovering cyanide from a cyanide-containing mixture. The process includes the steps of adjusting the pH of the cyanide-containing mixture to between about 6 to about 9.5, volatilizing the HCN contained in the pH adjusted mixture and contacting the volatilized HCN with basic material. Preferably, the cyanide recovery process is performed on tailings slurries resulting from metal recovery processes.

Abstract: A process for eluting gold-iodine complex from an ion-exchange resin, characterized by adding sulfuric acid and sodium nitrite to the gold-iodine complex adsorbed on the resin, and adding sodium sulfite as an eluant. The process is particularly useful for eluting gold-iodine complex adsorbed on strongly basic anion-exchange resin, such as washings resulting from the washing of leach residue which has been passed through the resin.

Abstract: Cyanide present in aqueous streams, such as effluents from electroplating and gold mining operations is reduced or elliminated by contacting the cyanide-containing stream with oxygen and carbon dioxide in the presence of cupric ions. The oxygen may be provided by air or oxygen and the contacting is carried out at until the pH of the aqueous stream is reduced to a value in the range of about 6 to 8 and preferably 6.5 to 7.5. Cupric sulfate has been found to be particularly effective for the described reaction.

Abstract: A process for removing and recovering cyanide from a cyanide-containing solution. The process includes the steps of adjusting the pH of the cyanide-containing solution to between about pH 6 and about pH 9.5, volatilizing the HCN contained in the pH adjusted solution and contacting the volatilized HCN with basic material. Preferably, the cyanide recovery process is performed on tailings slurries resulting from metal recovery processes.

Abstract: An agglomerative heap leaching method for recovering gold, silver or other metals from low grade refractory ores. Hypochlorite compounds are incorporated directly into the ore agglomerates as they are formed. This provides ample time and opportunity for the hypochlorite to destroy, modify or passivate refractory components of the ore thereby improving metal recovery in the subsequent cyanide leaching step.

Abstract: A system for heap leach mining comprises supply and header pipes for conducting a leaching solution alongside a bed or "heap" of crushed metal-laden ore deposited on an impervious pad. A series of spaced tubes are connected to the supply and header pipes to extend transversely thereof, over the pad, to receive the leaching solution therefrom. A plurality of emitters are connected in spaced relationship along each of the tubes for emitting the leaching solution at a controlled and substantially uniform rate over the pad and into the ore bed. At least some of the emitters are adjustable whereby different sets of flow passages can be utilized. The adjustable emitter comprises a sleeve slip-fit and rotatably mounted in a housing for rotative adjustment between at least two positions to alternately communicate the sets of flow passages with an inlet to the emitter.