Process for recycling chromium from waste water containing hexavalent chromium

A process for recycling chromium from waste water containing hexavalent chromium, comprising the following steps:

• (1) adjusting the pH value of the waste water containing chromium to 1.0-2.0 by using 10-50 wt % of sulfuric acid,
• then extracting hexavalent chromium contained in waste water to a trialkylamine-kerosene solution containing 30 wt % of trialkylamine as an extraction agent and kerosene as a solvent, and separating the organic phase from an aqueous phase to obtain the organic phase loaded with the hexavalent chromium, wherein the flow velocity ratio of aqueous phase to organic phase in extraction is (10-25):1;
• (2) reducing the hexavalent chromium in organic phase to trivalent chromium by using an aqueous solution of an organic reducing agent, performing reverse extraction to feed the trivalent chromium into the aqueous phase, and performing separation of aqueous phase and organic phase to obtain a solution containing the trivalent chromium and a regenerated organic phase, wherein the organic reducing agent is ethanol, the aqueous solution contains 50 wt % of ethanol, and the flow velocity ratio of aqueous phase to organic phase in reverse extraction is (1:1)-(1:5);
• and
• (3) performing solvent evaporation and then crystallization on the solution containing the trivalent chromium to recycle the trivalent chromium.