Study On The Fixation Of Heavy Metals In Copper Tailings And Tailings Improvement By Biocha

The large amount of copper tailings,coupled with the harm of heavy metals,poses a great threat to the ecological environment.As one of the reclamation methods,tailings improvement is of great significance to the utilization of tailings resources.In situ remediation of tailings by adding modifiers and regulators has become one of the important means of ecological environment restoration of tailings.Biochar has rich pore structure,oxygen-containing functional groups,high specific surface area and other excellent characteristics,which is of great significance for the immobilization and stabilization of heavy metals in copper tailings.In this paper,biochar was used as a modifier,and industrial solid waste copper tailings were used as the research object.Chemical and bioremediation methods were used to improve tailings by using different types of biochar（lignocellulose-based and sludge-based biochar）,of which copper tailings accounted for more than 90%.At the same time,the basic characteristics of biochar were improved by chemical modification,and its influence on the physical and chemical properties of tailings,especially the change of heavy metal occurrence forms,was studied.At the same time,combined with phytoremediation,tailings remediation was completed.By adding low-quality biochar（about 1.8%～2.0%）to copper tailings,the germination rate and survival rate of plants can be improved to a certain extent,and the fixation ability of heavy metals in copper tailings can be enhanced.Effectively reduce its bioavailability and reduce the release of unstable heavy metal forms.The experimental conclusions are as follows:（1）The sludge-based and lignocellulose-based biochars used in the experiment were different in basic physical and chemical properties such as specific surface area and functional group types.After adding biochar to copper tailings,the heavy metal copper in tailings can be better fixed and stabilized,and the extremely unstable weak acid extraction state can be transformed into stable oxidation state and residual state,thereby reducing the bioavailability and reducing the potential threat of heavy metals in tailings to the ecological environment.（2）Bioavailability indicators were used to compare the immobilization and stabilization effects of different types and different modification methods of biochar on heavy metal Cu,that is,the reduction of weak acid extraction and conversion efficiency.Among them,sludge-based biochar can significantly reduce the bioavailability of heavy metals in tailings,and the distribution rate of weak acid extractable heavy metals can be reduced from 49%to 23%,which significantly reduces the bioavailability.In contrast,lignocellulose-based biochar can better transform the distribution rate of various forms of heavy metals,that is,to the stable state.The weak acid extraction state is reduced from 50%to 27%,and the residual state is increased from 22%to 45%,which is beneficial to improve the immobilization and stabilization efficiency of heavy metals in tailings.（3）Using the heavy metal remediation efficiency index,the fixation and stabilization efficiency of two types of biochar on heavy metal Cu was compared.After determination,the repair efficiency of heavy metal Cu in the raw ore is about 20%.After adding biochar,400^oC sludge biochar can increase the repair efficiency to 34%.The heavy metal remediation efficiency of the two lignocellulosic-based biochars at500^oC is comparable,which can increase the efficiency to 40%.However,the remediation efficiency of biochar modified by Fe³⁺and KMn O₄is only about 22%.This may be due to the presence of Fe and Mn elements,which increases the ion exchange of heavy metals,and thus is more reducible and oxidizable,thus reducing the overall remediation efficiency of heavy metals.（4）The potential risk index of heavy metals in different groups was calculated,and it was found that unmodified biochar could significantly reduce this index.Among them,lignin cellulose-based biochar had the best effect.Combined with the remediation efficiency index of heavy metals,it showed that it had the highest morphological transformation efficiency of Cu to a certain extent,that is,the weak acid extraction state and the reducible state were unstable.The ability to transform into a stable oxidizable state and a residual state is high.（5）After adding biochar,it can effectively improve the germination rate and survival rate of the plant,improve the overall tailings soil condition,reduce the bulk density and increase the porosity,but there are also some phenomena of increasing the inhibition rate of seedling height,which may be related to the introduction of new ions,bring some pollution,and then inhibit the seedling height,so the average height of the plant is also relatively short.