Study On Pretreatment Process Of Chromium Plating Wastewater By Iron-Carbon Micro-electrolysis Technique

Investigation is given to how to effectively and economically pretreat chrome-plating effluent using iron-carbon micro-electrolysis technology in this study.With iron-carbon microelectrolysis as main means and polymerization ferric chloride?PFS?flocculation precipitation as the assisted,the chrome-plating effluent simulated from standard chromium stock solution,in concentration of 20 mg/L,is conducted with single factor test,while actual chrome-plating effluent is researched by single factor test and orthogonal test.The test results of simulated chrome-plating effluent suggest that:iron-carbon micro-electrolysis can remove more than 60%of the total chromium in simulated chrome-plating effluent and 99.99%at maximum,in spite of its poorer treatment effect as compared to iron-carbon microelectrolysis+PFS flocculation precipitation in most cases.PFS flocculation precipitation is conductive to the removal of total chromium in simulated chrome-plating effluent,while increases treatment cost and decreases the removal rates of the test groups with original high removal rate.The treatment effect of iron-carbon microelectrolysis+PFS flocculation precipitation is inhibited by excess Fe²⁺and Fe³⁺.This inference is further proved by the results of the single factor test of iron-carbon ratio on simulated chrome-plating effluent and the single factor test on actual chrome-plating effluent.In the case of the optimum reaction condition for single iron-carbon microelectrolysis on simulated chrome-plating effluent,including room temperature of 25?,pH value of 2,reaction time of 60 min,and iron-carbon ratio of 2:1,99.99%of the total chromium in the effluent can be removed.In the case of treating simulated chrome-plating effluent by iron-carbon microelectrolysis+PFS flocculation precipitation under the optimum conditions of room temperature of 25?,pH value of2,reaction time of 60 min,and iron-carbon ratio of 2:1,99.98%of the total chromium in the effluent can be removed.Actual chrome-plating effluent is conducted with single factor test using iron-carbon microelectrolysis and iron-carbon microelectrolysis+PFS flocculation precipitation.According to the results of single factor test using iron-carbon microelectrolysis,two level groups with higher treatment effect are selected for orthogonal test.Under the optimal conditions of iron-carbon microelectrolysis,including pH value of 2,iron-carbon ratio of 2:1?As for carbon powder,o.5 g is noted as 1?,stirrer temperature of 65?,and reaction time of 120 min,99.48%of the total chromium and22.39%of the COD_Cr in the effluent can be removed.According to the SEM analysis on the electroplating sludge produced by orthogonal test,the uneven surface of the sludge increases the contact area with effluent and thus facilitates the microelectrolysis of effluent.In addition,the reduction and flocculation precipitation of Cr⁶⁺are mainly observed on the surface of iron powder.