Study On The Process Of Electroplating Sludge Co-combustion-selective Leaching Of Valuable Metals

Electroplating sludge contains a large amount of valuable metals and toxic metals,which not only has certain resource value,but also causes certain harm and impact on the natural environment and human health.At present,electroplating sludge is mainly used to recycle valuable metals by fire and wet methods.However,these two processes have problems such as poor working environment,low product purity,long process flow,and secondary pollution.It is necessary to continue to develop more environmentally friendly and safer resource recovery processes.In this study,through the detection and analysis of five kinds of electroplating sludge collected,the target metal in electroplating sludge was determined and the corresponding disposal scheme was designed.The feasibility of bioleaching of electroplating sludge and the leaching mechanism of Ni,Cu,Zn and Cr were determined by bioacid direct leaching of electroplating sludge.The electroplating sludge was roasted to determine whether the target metal in electroplating sludge could be extracted step by step.The leaching residue was prepared into shale ceramsite to realize the full resource utilization of electroplating sludge.The main conclusions are as follows:1.The contents of Ni,Cu,Zn and Cr in the five kinds of electroplating sludge are high,and the main forms are acid soluble and reducible,while Cr is mostly in oxidizable and residual state.By comparing the five kinds of electroplating sludge with four leaching systems(bio-acid,H₂SO₄,H₂SO₄+Fe³⁺,H₂SO₄+Fe²⁺),the leaching rate of Cr in bio-acid system was higher than that in pure inorganic acid system.Through the analysis of the leaching residue characterization of different leaching systems,it is concluded that the leaching of Ni,Cu and Zn is mainly affected by H⁺,while the leaching of Cr is not only affected by H⁺in the biological acid,but also promoted by Fe³⁺,Fe²⁺and extracellular polymers.2.Bioleaching electroplating sludge,with the increase of solid-liquid ratio,leaching efficiency is declining.The combined treatment process is better than the single process,so the roasting pretreatment+bioleaching coupling process is designed.Compared with the single bioleaching process,the leaching efficiency and batch processing capacity of electroplating sludge are improved.The electroplating sludge was pretreated by roasting at400℃,and then leached by bio-acid with p H of 0.8.Under the condition of solid-liquid ratio of 20%,the leaching efficiency of Ni,Cu and Zn in more than 60%electroplating sludge reached 100%,and the leaching efficiency of Ni,Cu and Zn in less than 40%electroplating sludge was more than 90%,and the leaching rate of Cr and Fe was less than 70%.Provide experimental data for the subsequent selective leaching of target metals.3.The wet process of selective leaching of target metals from electroplating sludge is as follows:Al is preferentially leached from electroplating sludge by KOH solution,the dealuminate slag is mixed with the same amount of KOH,roasted at 800℃,and then Cr is selectively leached by water leaching,the dechromate slag is mixed with the same amount of NH₄Cl,and roasted at 400℃,Ni,Cu and Zn are selectively leached by water leaching,80%of Fe is left in the residue,the step-by-step leaching of target metals is basically realized,and the problem of separation of chromium and iron is solved.4.The electroplating sludge bioleaching leach residue was mixed with shale and calcined at 1150℃to prepare shale pellets.All the five shale pellets were able to meet the qualified requirements of the pellets,and the TCLP tests of the pellets met the national standard requirements and were able to be used as general construction materials.