An electrochemical process implements, in a decoupled manner, a first step of electrolysis of an electrolyte to produce gaseous oxygen in a chamber and a second step of electrochemical conversion of H+ ions into gaseous hydrogen in a chamber which contains a liquid phase and a gas phase not dissolved in the liquid phase. Gaseous hydrogen produced in the conversion step is partly present in the gaseous headspace of chamber and as bubbles in the electrolyte, and partly dissolved in the electrolyte which is saturated with hydrogen. The electrolyte has at least one redox pair (A/B) forming at least one intermediate vector enabling the decoupling of the first and second steps. The interface between the gas and liquid phases is increased during the second step to accelerate the diffusion, from liquid phase to gas phase, of the dissolved hydrogen able to supersaturate the electrolyte. Pressurized gaseous hydrogen is then collected.

The present invention is directed to an electrochemical device for at least partially removing or reducing a target ionic species from an aqueous solution using faradic immobilization, the electrochemical device including at least one first electrode and at least one second electrode with different void fraction and surface area properties, due to differences in void fraction (also referred to as void ratio) of the at least one first and the at least one second electrode, water flows through an electrode with a high porosity, while the aqueous solution does not flow through an electrode with a low porosity. The asymmetry of the electrodes provides a desired voltage distribution across the device, which equates to a different voltage at each electrode, to control the speciation of the target ionic species at the anode and the cathode.

Any metal having a low α-ray emission, the metal being any one of tin, silver, copper, zinc, or indium, wherein an emission of an α-ray after heating the metal at 100° C. in an atmosphere for six hours is 0.002 cph/cm.sup.2 or less. Any metal of tin, silver, copper, zinc and indium each including lead as an impurity is dissolved to prepare a hydrosulfate aqueous solution of the metal and lead sulfate is precipitated and removed in the solution. The lead sulfate is precipitated in the hydrosulfate aqueous solution by adding a lead nitrate aqueous solution including lead having an α-ray emission of 10 cph/cm.sup.2 or less to the hydrosulfate aqueous solution, from which the lead sulfate has been removed, and, at the same time, the solution is circulated while removing the lead sulfate to electrowinning the metal using the hydrosulfate aqueous solution as an electrolytic solution.

Any metal having a low α-ray emission, the metal being any one of tin, silver, copper, zinc, or indium, wherein an emission of an α-ray after heating the metal at 100° C. in an atmosphere for six hours is 0.002 cph/cm.sup.2 or less. Any metal of tin, silver, copper, zinc and indium each including lead as an impurity is dissolved to prepare a hydrosulfate aqueous solution of the metal and lead sulfate is precipitated and removed in the solution. The lead sulfate is precipitated in the hydrosulfate aqueous solution by adding a lead nitrate aqueous solution including lead having an α-ray emission of 10 cph/cm.sup.2 or less to the hydrosulfate aqueous solution, from which the lead sulfate has been removed, and, at the same time, the solution is circulated while removing the lead sulfate to electrowinning the metal using the hydrosulfate aqueous solution as an electrolytic solution.

A method for recovering metal zinc from a solid metallurgical waste containing zinc and manganese, may include: (a) bringing the solid metallurgical waste into contact with an aqueous leaching solution comprising chloride ions and ammonium ions to produce at least one leachate including zinc ions and manganese ions and at least one insoluble solid residue; (b) cementing the leachate, by adding metal zinc as a precipitating agent, to eliminate at least one metal other than zinc and manganese possibly present in the leachate as ions and producing a purified leachate; (c) subjecting the purified leachate to electrolysis in an electrolytic cell including at least one cathode and at least one anode immersed in the purified leachate to deposit metal zinc on the cathode and producing at least one exhausted leachate, and, before the electrolysis, precipitating manganese ions by oxidation with permanganate ions and subsequently separating a precipitate including MnO.sub.2.

A method for recovering metal zinc from a solid metallurgical waste containing zinc and manganese, may include: (a) bringing the solid metallurgical waste into contact with an aqueous leaching solution comprising chloride ions and ammonium ions to produce at least one leachate including zinc ions and manganese ions and at least one insoluble solid residue; (b) cementing the leachate, by adding metal zinc as a precipitating agent, to eliminate at least one metal other than zinc and manganese possibly present in the leachate as ions and producing a purified leachate; (c) subjecting the purified leachate to electrolysis in an electrolytic cell including at least one cathode and at least one anode immersed in the purified leachate to deposit metal zinc on the cathode and producing at least one exhausted leachate, and, before the electrolysis, precipitating manganese ions by oxidation with permanganate ions and subsequently separating a precipitate including MnO.sub.2.

An ammonium complex system-based method for separating and purifying lead, zinc, cadmium, and copper, comprising the following steps: a zinc-containing raw material is leached using a leach solution to produce a leached solution; a filtrate and a filter residue are produced by filtration; the filtrate is mixed with metal lead to displace copper, undergoes a solid-liquid separation to produce a first separated liquid, is mixed with metal cadmium to displace lead, undergoes a solid-liquid separation to produce a second separated liquid, is mixed with metal zinc to displace cadmium, and undergoes a solid-liquid separation to produce a third separated liquid; and, the third separated liquid is electrolyzed to produce metal zinc, and an electrolytic solution is returned to the leaching step.

An ammonium complex system-based method for separating and purifying lead, zinc, cadmium, and copper, comprising the following steps: a zinc-containing raw material is leached using a leach solution to produce a leached solution; a filtrate and a filter residue are produced by filtration; the filtrate is mixed with metal lead to displace copper, undergoes a solid-liquid separation to produce a first separated liquid, is mixed with metal cadmium to displace lead, undergoes a solid-liquid separation to produce a second separated liquid, is mixed with metal zinc to displace cadmium, and undergoes a solid-liquid separation to produce a third separated liquid; and, the third separated liquid is electrolyzed to produce metal zinc, and an electrolytic solution is returned to the leaching step.

A method, a system, and an apparatus for preparing manganese sulfate are provided. The method comprises introducing materials comprising a first stream, a second stream, and a reductant to a reactor to form a mixture. The first stream comprises a sulfate-containing acid, and the second stream comprises a manganese oxide compound. At least a portion of the mixture is reacted to provide a reactor outlet stream comprising an aqueous portion and an undissolved portion. The method comprises separating at least a portion of the aqueous portion from the undissolved portion in the reactor outlet stream to produce an aqueous stream comprising manganese sulfate and an undissolved stream.

A method, a system, and an apparatus for preparing manganese sulfate are provided. The method comprises introducing materials comprising a first stream, a second stream, and a reductant to a reactor to form a mixture. The first stream comprises a sulfate-containing acid, and the second stream comprises a manganese oxide compound. At least a portion of the mixture is reacted to provide a reactor outlet stream comprising an aqueous portion and an undissolved portion. The method comprises separating at least a portion of the aqueous portion from the undissolved portion in the reactor outlet stream to produce an aqueous stream comprising manganese sulfate and an undissolved stream.