Effects Of Silicate Bacteria On Activation Of Silicon And Stabilization Of Heavy Metals In Electrolytic Manganese Residue

Electrolytic manganese residue?EMR?is a potentially harmful industrial solid waste produced in the process of electrolytic manganese production.There are more than 60 million tons of EMR in China with a annual growth rate of 10 million tons,which seriously restricts the development of electrolytic manganese industry.On the one hand,EMR contains a lot of beneficial elements,if it can be extracted with appropriate methods,it can be recycled as useful resources.In addition,EMR contains some heavy metal elements and compounds.Therefore,in order to improve the degree of harmfulless treatment and utilization of mineral resource,extracting useful elements from EMR has economic benefits,stabilizing the poisonous and harmful metallic elements in EMR has environmental benefits.If the appropriate methods can be chosen to implement both requirements,and it is available to realize the the source treatment of the large mining waste,and is the key to promote the sustainable development of electrolytic manganese industry.Silicon is an important element in plant growth and plays as an important mechanical and physical barrier in plant growth,especially under stress conditions.EMR is a kind of industrial solid waste with high silicon content,but most silicon exists in silicate minerals with very low water solubility,usually,called inactive silicon,which cannot be directly absorbed and utilized by plants.Therefore,the development of an efficient and environmentally friendly silicon activation process for EMR is very important for the reuse of the solid waste and environmental sustainability.The purpose of this study is to investigate the leaching effect of silicate bacteria on EMR and the transformation rules of silicon and heavy metals in the leaching solution during bioleaching.In addition,the study reveals the activation mechanism of silicon and stabilization mechanism of heavy metals in electrolytic manganese residue.The specific research contents and conclusions are summarized as follows:?1?Parameter optimization of available silicon during bioleaching.This part explored the influence of single silicate bacteria and mixed bacteria on the improvement of available silicon in the process of bioleaching,and investigated the effect of leaching time,temperature,pH,pulp density,rotational speed and particle size through shake flask test.The results show that the mixed bacteria under the conditions:temperature of 30 ^oC,initial pH of 7.0,particle size of 0.150 mm,pulp density of 5%,rotational speed of 180 rpm,leaching time 20 d,the available silicon content in the bioleaching system increased from 5 mg?L^-1 to 160 mg?L^-1.While the single bacteria can only achieve 140 mg?L^-1.The result indicated that silicate bacteria have an obvious effect on the activation of silicon in EMR,and the mixed bacteria have better effect than single bacteria.Our research finding indicated the possibility of resource utilization of EMR.The leachate and residue were characterized by FT-IR,XRD and SEM.?2?Variations in the physicochemical properties of heavy metals during bioleaching.In this part,the variations of the contents of heavy metals,Mn,Co,Pb and Ni,in the leaching solution during the action of single and mixed bacteria were studied respectively.The result showed that the contents of heavy metals in the solution tend to decrease in the process of bioleaching.The modified BCR sequential extraction was used to study the changes in the chemical form of heavy metals in residue,indicating that several heavy metals tend to stabilize after 20 days of bioleaching,especially for Mn with the highest environmental toxicity.The leaching toxicity of heavy metals in EMR before and after bioleaching was analyzed,and the leaching concentration of Mn decreased from 1960 mg?L^-1 to 815 mg?L^-1.The results show that bioleaching can provide theoretical support for the innocuity of heavy metals in EMR.?3?Activation mechanism of silicon in EMR.The results showed significant variation on the leaching effect of silicate bacteria on different silicate minerals.And the dissolution of silicate minerals is not only related to the metabolites of bacteria,but also related to the growth of silicate bacteria on the mineral surface.The activation mechanism of silicon in EMR is the combined action of microorganisms and their metabolites,including the decomposition of mineral by the growth of silicate bacteria on mineral surface,as well as the acid dissolution and complexation of metabolites.?4?Stabilization mechanism of heavy metals in EMR.The results showed that the stabilization mechanism of heavy metals in EMR includes two aspects:the effect of available silicon on heavy metals in the leaching solution and the effect of silicate bacterial metabolites on heavy metals.The bioleaching system with higher silicon content is more conducive to the formation of stable precipitates by binding metals,and the content of free heavy metals in the solution is reduced.In addition,organic acids,amino acids,polysaccharides and other substances produced by silicate bacteria can promote the stabilization of heavy metals in EMR through coordination and complexation reactions.