Methods of Treatment of Chromite Ore Processing Residue

Abstract

Methods to reduce hexavalent chromium (Cr(VI)) in chromite processing wastes include one or more of the following steps: contacting the chromite processing wastes with an oxygen scavenger or chemical reducer; permitting the chromite processing wastes to react with the oxygen scavenger or chemical reducer; contacting the chromite processing wastes with ferrous ion; contacting the chromite processing wastes with sulfide ion; and, contacting the chromite processing wastes with ferrous sulfide.

1 - 75 . (canceled) 
     
     
         76 . A method for reducing chromium (VI) in an underground deposit of chromium ore processing residue, comprising: injecting a ferrous liquid into the underground deposit of chromium ore processing residue, with the underground deposit comprising solid residue particles, and with pore spaces between particles, with the ferrous liquid reducing the pH of the pore water to less than about 7, and with the volume of ferrous liquid injected sufficient to substantially fill the pore spaces between the particles; waiting until the pH of the injected ferrous liquid increases to a pH of about 9; and then injecting a sulfide solution into the underground deposit. 
     
     
         77 . The method of  claim 76  with the ferrous liquid comprising ferrous chloride or ferrous sulfate, and with ferrous in the liquid precipitating out as ferrous hydroxide with the increase in the pH, and with the ferrous hydroxide then dissolving into the sulfide solution and re-precipitating out as ferrous sulfide. 
     
     
         78 . The method of  claim 76  further comprising measuring the pH the liquid in the deposit. 
     
     
         79 . The method of  claim 76  further comprising measuring pH of COPR samples treated with the ferrous treatment chemicals and determining time taken to achieve a desired pH. 
     
     
         80 . The method of  claim 76  further comprising waiting a predetermined time interval. 
     
     
         81 . The method of  claim 76  wherein the ferrous liquid comprises ferrous chloride or ferrous sulfate and the sulfide solution comprises sodium sulfide. 
     
     
         82 . The method of  claim 76  with the ferrous liquid comprising ferrous chloride or ferrous sulfate including up to %5 excess acid.