Fundamental Research On The Treatment Of Typical Mineral Processing Wastewater By Electrocoagulation

As a large country with rich mineral resources,the exploitation and utilization of mineral resources is a guarantee for China’s national economic and social development.However,significant amounts of wastewater containing high concentration of contaminants such as flotation reagents（contributor to COD,colletors mainly）and suspended solids is generated during beneficiation processes.Direct discharge of the mineral processing wastewater may seriously threaten mine environment,so the wastewater should be treated properly to meet the requirement of discharge or reuse.Currently,the widely used methods in the processing plants such as neutralization and coagulation–flocculation have the limitations such as low efficiency,risk of secondary pollution.Electrocoagulation（EC）,due to the unique advantages including high efficiency,reduced sludge generation and avoid addition of chemicals,has been widely used in various wastewater treatments such as dyeing wastewater,paper industry wastewater,and oily wastewater.Given these considerations,the removal of typical collectors used in the flotation of oxidized minerals and sulphide minerals by EC was investigated in this paper.First,selecting the anode materials properly could achieve the effective removal of different collectors and the effect of suspended micro-grained mineral particles on the EC performance was studied.Second,the removal mechanisms for different collectors were discussed systematically.Finally,a novel EC reactor by using aluminum scraps as anode materials was designed and successfully employed for the treatment of real mineral processing wastewater obtained from a non-ferrous metal mineral processing plant.The main results of the paper are concluded as follows:（1）Selection of anode materials is the key to remove different types of collectors from mineral processing wastewater.Fe/Al-EC can effectively remove sodium solution.Al-EC can achieve the removal of benzohydroxamic acid（BHA）,while Fe-EC technology is ineffective.However,Al/Fe-EC are both infeasible to remove the collectors of sulfide minerals including butyl potassium xanthate（BX）and sodium diethyldithiocarbamate（DDTC）,while using Cu as anode can achieve good performance.（2）The COD removal from sodium oleate and BHA solutions by Al/Fe-EC was investigated.In the case of sodium oleate,during the early stage of Al/Fe-EC treatment,the generated particles are in colloidal state,resulting in the increasment of solution turbidity.With increasing electrolysis time,the colloidal stability is destroyed,which leads to the sedimentation of particles and effective removal of COD.Some fine minerals such as calcite can accelerate the sedimentation of EC flocs,thereby improving COD removal efficiency.However,the presence of water glass will adversely affect EC performance by increasing the stabilization of the systems.Compared with sodium oleate,the COD removal of BHA solution by Al-EC is much slower.During the EC process,the turbidity of BHA solution remains low.Besides,the presence of suspended fine minerals and water glass has less effect on the EC performance.（3）The mechanisms for the removal of sodium oleate and BHA by Al/Fe-EC were revealed.The involved mechanisms for sodium oleate removal varies with intial p H.At p H<8.9,liquid HOl_（l）is the predominant specie and the COD can be removed quilkly due to the demulsification of EC;At p H>8.9,Fe²⁺/Fe³⁺or Al³⁺generated from the anodes can react with Ol^-to form insoluble oleate with high surface potentials which is difficult to settle.As electrolysis proceeds,the insoluble oleate can be removed by double-layer compression and charge neutralization.In the case of BHA solution,Fe²⁺/Fe³⁺or Al³⁺generated in the EC reactor can react with BHA to form metal-collector complexes.However,with the increasing of OH^-concentration（hydrogen evolution reaction）,the generation of metallo-organic complexes shows a dropping tendency.Besides,the BHA-Fe complex has a good solubility especially in high alkaline solution.However,Al-EC process exhibits some p H buffering capacity and the insoluble complex BHA-Al can be removed through sweep coagulation or interparticle bridging by the aluminum hydroxide.（4）The COD removal from BX and DDTC solutions by Cu-EC was investigated.During EC process,the turbidity of BX solution first increases then decreases due to the generation of colloidal suspensions.Fine calcite or fluorite particles can improve the EC performance by accelerating the sedimentation of the generated flocs.The flocs generated in DDTC solution has better sedimentation property,resulting in low solution turbidity during entire EC time.The presence of fine pyrite can improve the EC removal efficiency.（5）The mechanisms for the removal of BX and DDTC by Cu-EC were revealed.Cu²⁺generated in suit can combine with the S site of sulfydryl in BX or DDTC to form insoluble metal-collector salt,which can be removed from solution by settling with copper oxide/hydroxide after EC.（6）A novel EC reactor by using aluminum scraps as anode materials has been successfully used in the treatment of real minerals processing wastewater obtained from a non-ferrous metal mineral processing plant in Hunan.COD and turbidity removal efficiency were found as 73.5%and>99%,respectively.EC performed better than chemical coagulation methods.