Study On Sulfuric Acid Leaching Process Of Chromite And Waste Residue Recycling

Chromium salt industry rapidly growing in China causing a increasing pollution of Cr(VI)-bearing waste,which is still a unavoidable problem in the current chromium salt preparation process.The sulfuric acid leaching process provides a new idea for the clean preparation of chromium salt,which can effectively avoid the generation of Cr(VI)during the process of chromium salt production,and solve the problem of Cr(VI)pollution from the source.On this basis of the chemical composition of natural chromite,various binary spinel of magnesium-aluminate spinel,magnesium-ferric spinel and magnesium-chromium spinel were prepared and used in the investigation of effects of Cr(VI)on chromite decomposition in the hot concentrated sulfuric acid solution.Moreover,with the goal to recycle the waste residue produced in the sulfuric acid leaching process,an experimental study on the recovery of anhydrous chromium sulfate by employing ammonium sulfate treatment was carried out.A Box-Behnken Design was used,and the effects of temperature,pH value of solution and ammonium sulfate dosage on the recovery efficiency of anhydrous chromium sulfate were investigated.The main conclusions of this study are as follows:(1)Magnesium-aluminate spinel,magnesium-ferric spinel and magnesium-chromium spinel can be partially dissolved in the hot concentrated sulfuric acid.The usage of Cr(VI)can significantly improve the decomposition rate of magnesium-chromium spinel,while has no notable influence on the decomposition rate of magnesium-aluminate spinel and magnesium-ferric spinel.(2)The reaction mechanism of Cr(VI)to magnesium-chromium spinel is redox-type catalytic decomposition.By reacting with Cr(VI)to form intermediates,the stability of magnesium-chromium spinel structure is reduced and the decomposition of spinel is promoted.(3)A 3D response surface model was established,and the model was analyzed and verified by variance analysis and experiments.The findings showed that the model results had a high fitting degree with the experimental data.Based on the model optimization,an optimum processing parameters for recycling anhydrous chromium sulfate was proposed:the temperature is 87 ?,the pH value is-0.8,the molar ratio of actual dosage of ammonium and theoretical dosage of ammonium is 2:1.(4)The separation and extraction tests for different phases from waste residue were carried out in this work.On the basis of experimental results,a new process for recycling treatment of waste residue produced in sulfuric acid leaching process of chromite was proposed.