A method for making an aqueous hypochlorous acid (HClO) solution includes electrolyzing a solution of sodium chloride to produce a solution of sodium hypochlorite; and producing the aqueous hypochlorous acid solution by adjusting a pH of the solution of sodium hypochlorite to a value within a range of 3 to 8 by adding a selected weak acid to the solution of sodium hypochlorite to produce a buffer including the selected weak acid and a salt of the selected weak acid.

The recovery of noble metal(s) from noble-metal-containing material is generally described. The noble metal(s) can be recovered selectively, in some cases, such that noble metal(s) is at least partially separated from non-noble-metal material within the material. Noble metal(s) may be recovered from noble-metal-containing material using mixtures of acids, in some instances. In some cases, the mixture can comprise nitric acid and/or another source of nitrate ions and at least one supplemental acid, such as sulfuric acid, phosphoric acid, and/or a sulfonic acid. The amount of nitrate ions within the mixture can be, in some instances, relatively small compared to the amount of supplemental acid within the mixture. In some cases, the recovery of noble metal(s) using the acid mixtures described herein can be enhanced by transporting an electric current between an electrode and the noble metal(s) of the noble-metal-containing material. In some cases, acid mixtures can be used to recover silver from particular types of scrap materials, such as scrap material comprising silver metal and cadmium oxide and/or scrap material comprising silver metal and tungsten metal.

The recovery of noble metal(s) from noble-metal-containing material is generally described. The noble metal(s) can be recovered selectively, in some cases, such that noble metal(s) is at least partially separated from non-noble-metal material within the material. Noble metal(s) may be recovered from noble-metal-containing material using mixtures of acids, in some instances. In some cases, the mixture can comprise nitric acid and/or another source of nitrate ions and at least one supplemental acid, such as sulfuric acid, phosphoric acid, and/or a sulfonic acid. The amount of nitrate ions within the mixture can be, in some instances, relatively small compared to the amount of supplemental acid within the mixture. In some cases, the recovery of noble metal(s) using the acid mixtures described herein can be enhanced by transporting an electric current between an electrode and the noble metal(s) of the noble-metal-containing material. In some cases, acid mixtures can be used to recover silver from particular types of scrap materials, such as scrap material comprising silver metal and cadmium oxide and/or scrap material comprising silver metal and tungsten metal.

A method for cleanly extracting metallic silver includes: mixing an acidic solution containing Ce.sup.4+ and NO.sub.3.sup.− with a silver-containing material for leaching; after the leaching is completed, carrying out a solid-liquid separation to obtain a leaching solution containing Ce.sup.3+ and Ag.sup.+; and electrolyzing the leaching solution, wherein an oxidation reaction of Ce.sup.3+ occurs at an anode to realize a regeneration of Ce.sup.4+ and an electrolytic reduction occurs at a cathode to reduce Ag.sup.+ to obtain the metallic silver. Ce.sup.4+ is used as a leaching agent and an intermediate oxidant to implement a cyclic operation of solution leaching and electrolytic regeneration on the silver-containing material. Almost no NO.sub.x and waste liquid are caused by the extraction process, and the invention is clean and environmentally friendly.

A method for generating a metallic particle slurry in a regenerator, the method comprising the steps of: (a) generating metallic particles on a surface of a cathode by applying a forward current for a forward current period; (b) displacing the metallic particles from the surface of the cathode by applying a displacement force for a displacement period; (c) dissolving residual metallic particles by applying a reverse current for a reverse current period; (d) providing a plurality of regenerator cells; and (e) establishing an airlock by isolating aqueous electrolyte between cavities of regenerator cells.

A method for generating a metallic particle slurry in a regenerator, the method comprising the steps of: (a) generating metallic particles on a surface of a cathode by applying a forward current for a forward current period; (b) displacing the metallic particles from the surface of the cathode by applying a displacement force for a displacement period; (c) dissolving residual metallic particles by applying a reverse current for a reverse current period; (d) providing a plurality of regenerator cells; and (e) establishing an airlock by isolating aqueous electrolyte between cavities of regenerator cells.

System for, and methods of, recovering precious metals from precious metals-containing solids are described herein. Methods for the recovery of precious metals from precious metals-containing solids heating a salt mixture to form a molten salt mixture, adding a precious metals-containing solid to the molten salt mixture to form a molten salt/precious metals-containing solids mixture, adding an oxidizing agent to the molten salt/precious metals-containing solids mixture, forming a liquid solution from molten salt/precious metals-containing solids mixture, the liquid solution comprising soluble precious metal salts, and subjecting the liquid solution to an electrodeposition process to form purified precious metals. Systems for, and methods of, recovery precious metals from precious metals-containing solids allow for the recovery of salt mixtures and reuse of the salt mixtures in subsequent precious metals recovery operations.

An environmentally friendly (e.g. no acid, base, or cyanide) system and process for large scale extraction of metal ion into aerobic molten salt (or ionic liquid) and the electrodeposition of metal (e.g. copper, gold, silver, etc.) from the metal ion dissolved in the molten salt. The non-volatile low vapor pressure liquid salt is reusable, and heat from the molten slag can heat the molten salts or ionic liquids. Another embodiment comprises a one-pot apparatus for the extraction of metal (e.g. copper) from metal earths and electrodepositing the metal using a low melting (209° C.) aerated Na—K—Zn chloride salt in which copper metal oxidizes and is converted to soluble copper chloride. When an electrical power supply is connected to the graphite vessel (cathode) and to copper rods in the melt (anodes), then the copper chloride is deposited as copper metal by electroreduction on the bottom of the graphite reaction vessel.

A filter press device for electrolytic production of metal for electrodeposition of metal from solutions, constructed from a plurality of cells connected electrically and hydraulically in series. Each has alternating frames and ion-exchange membranes to form alternating anode and cathode compartments, allowing the free path of liquid. Anolyte or catholyte passes through each compartment. The electrolyzed product is discharged from the compartment in the form of metal or a metallic compound. The electrodes are designed with a vertical base plate acting as an anode with the respective anolyte in a cell unit and in the other, acting as a cathode with the respective catholyte in the adjacent cell unit. Completed the production cycle, the device is stopped, the cell is opened, allowing the metal deposition electrodes, cathodes, can be removed and replaced to start a new productive cycle or remain in place with automatic detachment of metal product.

A filter press device for electrolytic production of metal for electrodeposition of metal from solutions, constructed from a plurality of cells connected electrically and hydraulically in series. Each has alternating frames and ion-exchange membranes to form alternating anode and cathode compartments, allowing the free path of liquid. Anolyte or catholyte passes through each compartment. The electrolyzed product is discharged from the compartment in the form of metal or a metallic compound. The electrodes are designed with a vertical base plate acting as an anode with the respective anolyte in a cell unit and in the other, acting as a cathode with the respective catholyte in the adjacent cell unit. Completed the production cycle, the device is stopped, the cell is opened, allowing the metal deposition electrodes, cathodes, can be removed and replaced to start a new productive cycle or remain in place with automatic detachment of metal product.