A process for recovering chromium from hexavalent chromium-containing wastewater comprises the following steps: (1) extracting hexavalent chromium in wastewater to an organic phase by using an extracting agent, and separating hexavalent chromium from a water phase, so as to acquire a hexavalent chromium-loaded organic phase; (2) reducing the hexavalent chromium-loaded organic phase by using an aqueous solution of an organic reducing agent, reducing hexavalent chromium into trivalent chromium, reversely extracting trivalent chromium into the water phase, and separating the organic phase from the water phase to acquire a solution of the trivalent chromium and a renewable organic phase, wherein the organic reducing agent is one or a mixture of alcohols, aldehydes and carboxylic acids having the carbon atom number ranging 1 to 3; and (3) performing solvent evaporation on the solution of trivalent chromium, catalyzing, and recovering the trivalent chromium.

A process for recovering chromium from hexavalent chromium-containing wastewater comprises the following steps: (1) extracting hexavalent chromium in wastewater to an organic phase by using an extracting agent, and separating hexavalent chromium from a water phase, so as to acquire a hexavalent chromium-loaded organic phase; (2) reducing the hexavalent chromium-loaded organic phase by using an aqueous solution of an organic reducing agent, reducing hexavalent chromium into trivalent chromium, reversely extracting trivalent chromium into the water phase, and separating the organic phase from the water phase to acquire a solution of the trivalent chromium and a renewable organic phase, wherein the organic reducing agent is one or a mixture of alcohols, aldehydes and carboxylic acids having the carbon atom number ranging 1 to 3; and (3) performing solvent evaporation on the solution of trivalent chromium, catalyzing, and recovering the trivalent chromium.

A charged material containing alloy iron of at least one of ferrochrome containing metallic Si or ferrosilicon, and unreduced slag containing Cr oxide generated by oxidative refining, is charged into an electric furnace as a mixture in which a mass ratio of a metallic Si amount to a Cr oxide amount is from 0.30 to 0.40, and a C concentration is in a range of from 2.0% by mass to a saturation concentration, and molten iron containing Cr obtained due to the Cr oxide undergoing reduction processing is produced, such that, when the charged material is heated and melted in the electric furnace, an attainment temperature is set to from 1400° C. to 1700° C., a maximum average heating rate in any 80° C. interval from 1300° C. to the attainment temperature is set to 15.0° C./min or less, and a minimum average heating rate in any 80° C. interval from 1300° C. to the attainment temperature is set to 3.0° C./min or greater.

A charged material containing a metal raw material of at least one of ferrochromium containing metal Si or ferrosilicon and unreduced slag containing Cr oxide generated by oxidation refining is charged into an AC electric furnace including three electrodes, a mass ratio of a metal Si amount to a Cr oxide amount being from 0.30 to 0.40, and a C concentration being from 2.0% by mass to a saturation concentration, and operation is performed under a condition where a diameter PCD (m) of a circle passing through the centers of the three electrodes viewed in a plan view from a central axis direction of the electric furnace, an average electrode height H.sub.e (m) that is a vertical distance from a tip of each electrode to a molten metal surface, a furnace inner diameter D.sub.f (m), a molten slag thickness H.sub.s (m), a spreading diameter D.sub.arc (m) of an arc on the molten metal surface, and a deflection angle θ (deg) of the arc satisfy the following relationships to produce molten iron containing Cr.

D.sub.arc=PCD+2H.sub.e.Math.tan θ

θ=52.5−75.Math.(PCD/D.sub.f)

0.22≤D.sub.arc/D.sub.f≤0.30

0.35≤H.sub.e/H.sub.s≤1.50

Described is a process of extracting metals from a wet mass which comprises: a step A of concentrating the metals in a carbonaceous solid by means of a thermochemical treatment of the wet mass, with the ancillary production of a treatment gas; a step B of thermochemical decomposition of the carbonaceous solid in an atmosphere constituted by an operating gas which contains oxygen in substoichiometric quantity to carry out the thermochemical decomposition in order to promote a combination of the metals with substances present in the carbonaceous solid to form salts and others solid compounds and to concentrate the latter in residual ashes of the carbonaceous solid at the same time providing for the formation of a combustible synthesis gas comprising hydrocarbons from the carbonaceous solid; a step C of extraction of the metals from the ashes produced.

Systems and methods for sequestering carbon, evolving hydrogen gas, producing iron oxide as magnetite, and producing magnesium carbonate as magnesite through sequential carbonation and serpentinization/hydration reactions involving processed olivine- and/or pyroxene-rich ores, as typically found in mafic and ultramafic igneous rock. Precious or scarce metals, such nickel, cobalt, chromium, rare earth elements, and others, may be concentrated in the remaining ore to facilitate their recovery from any gangue material.

Systems and methods for sequestering carbon, evolving hydrogen gas, producing iron oxide as magnetite, and producing magnesium carbonate as magnesite through sequential carbonation and serpentinization/hydration reactions involving processed olivine- and/or pyroxene-rich ores, as typically found in mafic and ultramafic igneous rock. Precious or scarce metals, such nickel, cobalt, chromium, rare earth elements, and others, may be concentrated in the remaining ore to facilitate their recovery from any gangue material.

Processes for producing low-nitrogen metallic chromium or chromium-containing alloys, which prevent the nitrogen in the surrounding atmosphere from being carried into the melt and being absorbed by the metallic chromium or chromium-containing alloy during the metallothermic reaction, include vacuum-degassing a thermite mixture comprising metal compounds and metallic reducing powders contained within a vacuum vessel, igniting the thermite mixture to effect reduction of the metal compounds within the vessel under reduced pressure i.e., below 1 bar, and conducting the entire reduction reaction in said vessel under reduced pressure, including solidification and cooling, to produce a final product with a nitrogen content below 10 ppm. The final products obtained, in addition to low-nitrogen metallic chromium in combination with other elements, can be used as raw materials in the manufacture of superalloys, stainless steel and other specialty steels whose final content of nitrogen is below 10 ppm.

Processes for producing low-nitrogen metallic chromium or chromium-containing alloys, which prevent the nitrogen in the surrounding atmosphere from being carried into the melt and being absorbed by the metallic chromium or chromium-containing alloy during the metallothermic reaction, include vacuum-degassing a thermite mixture comprising metal compounds and metallic reducing powders contained within a vacuum vessel, igniting the thermite mixture to effect reduction of the metal compounds within the vessel under reduced pressure i.e., below 1 bar, and conducting the entire reduction reaction in said vessel under reduced pressure, including solidification and cooling, to produce a final product with a nitrogen content below 10 ppm. The final products obtained, in addition to low-nitrogen metallic chromium in combination with other elements, can be used as raw materials in the manufacture of superalloys, stainless steel and other specialty steels whose final content of nitrogen is below 10 ppm.

A method and system for recovering a high yield of low carbon ferroalloy, e.g., low carbon ferrochrome, from chromite and low carbon ferrochrome produced by the method. A stoichiometric mixture of feed materials including scrap aluminum granules, lime, silica sand, and chromite ore are provided into a plasma arc furnace. The scrap aluminum granules are produced from used aluminum beverage containers. The feed materials are heated, whereupon the aluminum in the aluminum granules produces an exothermic reaction reducing the chromium oxide and iron oxide in the chromite to produce molten low carbon ferrochrome with molten slag floating thereon. The molten low carbon ferrochrome is extracted, solidified and granulated into granules of low carbon ferrochrome. The molten slag is extracted, solidified and granulated into granules of slag.