An electrochemical system and process are provided to convert an amount of chalcopyrite (CuFeS.sub.2) to a product including copper ions. In an electrochemical reactor, a potential is applied across an anode and a cathode to convert the chalcopyrite to an intermediate, chalcocite (Cu.sub.2S). The anode is covered to prevent contact with the intermediate, thus limiting subsequent conversion of the intermediate to covellite (CuS) in favor of conversion to a material more suited to chemical oxidation, cuprite (Cu.sub.2O). For example, the anode can be covered with one or more layers of filter paper. Upon application of an oxidizing agent, the cuprite is oxidized to produce a product including copper ions. The cathode and covered anode allow for efficient and inexpensive processing. The cost of this technique is comparable to industry standards, and moreover, has a much smaller environmental footprint than heat-based copper extraction.

This disclosure provides systems, methods, and apparatus related to nanoparticle/ordered-ligand interlayers. In one aspect, a structure comprises an assembly and a layer of ligands disposed on a surface of the assembly. The assembly comprises a plurality of metal nanoparticles. The metal nanoparticles of the plurality of metal nanoparticles in the assembly are proximate one another. The layer of ligands is operable to detach from the surface of the assembly but to remain proximate the surface of the assembly when the assembly is disposed in an electrolyte and a negative bias is applied to the assembly. An interlayer forms between the assembly and the layer of ligands, with the interlayer comprising desolvated cations from the electrolyte.

The invention is directed to a process to convert carbon dioxide to methane by contacting an aqueous solution comprising dissolved carbon dioxide with an electron charged packed bed comprising of a carrier, suitably activated carbon granules, and a biofilm of microorganisms under anaerobic conditions, wherein more than 90 mol % of the dissolved carbon dioxide in the aqueous solution is present as a bicarbonate ion and/or as a carbonate ion.

A three-dimensional photo/electrodialysis unit includes four compartments. A first compartment holds a three-dimensional electrode and a group of one or more electrochemically active redox species. A first electroactive cation selective membrane couples the first compartment to a second compartment that provides a first feedstock. An electroactive anion selective membrane couples the second compartment to a third compartment that provides a second feedstock. And a second electroactive cation selective membrane couples the third compartment to a fourth compartment

A three-dimensional photo/electrodialysis unit includes four compartments. A first compartment holds a three-dimensional electrode and a group of one or more electrochemically active redox species. A first electroactive cation selective membrane couples the first compartment to a second compartment that provides a first feedstock. An electroactive anion selective membrane couples the second compartment to a third compartment that provides a second feedstock. And a second electroactive cation selective membrane couples the third compartment to a fourth compartment that holds a second group of one or more electrochemically active redox species.

The invention is directed to a process to convert carbon dioxide to methane by contacting an aqueous solution comprising dissolved carbon dioxide with an electron charged packed bed comprising of a carrier and a biofilm of microorganisms under anaerobic conditions wherein the pH of the aqueous solution is above 7.5 and wherein the aqueous solution comprises between 0.3 and 4 M sodium cations or between 0.3 and 4 M sodium and potassium cations and more than 20 mM phosphate ions.

Described are electrochemical systems and methods for the generation of high purity hydride gases, e.g. for delivery to semiconductor fabrication reactors.