Effect Of Bagasse And Vermicompost Addition On The Microenvironment Of Electrolytic Manganese Residue Substrate

Electrolytic manganese residue is a solid waste produced in the process of electrolytic manganese metal with sulfuric acid leaching manganese carbonate ore powder.It not only takes up a large amount of land resources,but also causes serious soil,water and air pollution problems.With the increase of the output of electrolytic manganese residue and the improvement of national environmental protection requirements,soil matrix improvement has become the key to solve the problems of land reclamation and ecological restoration in mineral wasteland.In order to explore the matrix improvement of electrolytic manganese residue and promote the remediation of electrolytic manganese residue soil,this study selected bagasse and vermicompost as the matrix modifier,and studied the effect of matrix improvement at five time points(60d,90d,120d,180d,360d)under nine treatment methods,including:1)electrolytic manganese residue(CK);2)bagasse 4%(B1);3)bagasse 8%(B2);4)vermicompost 4%(V1);5)vermicompost 8%(V2);6)bagasse4%+vermicompost4%(V1B1);7)bagasse4%+vermicompost8%(V1B2);8)bagasse8%+vermicompost4%(V2B1);9)bagasse8%+vermicompost8%(V2B2)The effects of different treatments on the physical and chemical properties of electrolytic manganese residue,the formation and stability of aggregates and the forms of heavy metals were studied,and the effects of different treatments on the catalase activity,sucrase activity,urease activity,alkaline phosphatase activity,and the dynamic change characteristics of microbial diversity and community of electrolytic manganese residue were studied.To investigate the effects of bagasse and vermicompost on the substrate microenvironment of electrolytic manganese residue,and to reveal the remediation effect of vermicompost and bagasse on the soil chemistry of electrolytic manganese residue,so as to provide a reference basis for soil remediation of mineral wasteland.The main findings are as follows:(1)As time goes on,the pH value of electrolytic manganese residue gradually decreased.After 360d treatment,the pH value of V2B2 treatment decreased to 8.01,realizing the transformation from heavy alkalization to light alkalization;The electrical conductivity(EC)showed a downward trend,and the electrolytic manganese residue changed from heavy salinization to non-salination;After 180d,the content of soil organic carbon(SOC)increased 2-7 times,and the content of soil organic carbon in V2B2 treatment increased the highest(694%);With the prolongation of treatment time,the total nitrogen(TN)basically remained stable during 120-360 days of treatment.At 360d the V2B2 treatment increased by 610%compared with the CK treatment;the content of nitrate nitrogen(NO3--N)and ammonia nitrogen(NH4+-N)in each treatment was lower than that in the CK treatment;There was no significant difference in total phosphorus(TP)among different treatments,V2 treatment has the best treatment effect;When treated for 180d,the increase of available phosphorus(AP)in each treatment was 31%-66%compared with the CK treatment,V2B1 treatment has the best treatment effect.(2)The distribution of soil aggregates,under the condition of dry sieving,the aggregate content of each treatment is mostly concentrated in the particle size of>2mm.After 360d,each treatment is basically stable,among which the V2B2 treatment has the largest content of macroaggregates.Under the condition of wet sieving due to the instability of electrolytic manganese residue itself and the scouring effect of water power,the aggregate content is mainly concentrated in the size fractions of 2～1mm and 1～0.5mm;MWD,ELT and PAD under different treatments showed that the V2B2 treatment had the best effect.(3)Soil quality was evaluated based on Pearson correlation analysis as well as principal component analysis,and total nitrogen(TN),available phosphorus(AP)and mean weight diameter(MWD)were screened as the minimum data set for soil quality evaluation(SQI).The results showed that bagasse and vermicompost could effectively improve soil quality,with the best soil quality under V2B2 treatment at 360d.(4)The results of massive element and heavy metal morphology distribution of electrolytic manganese residue show that Mg mainly exists in exchangeable state and combined state of ferromanganese oxide,with strong activity;Ca,Mn,Cu,Fe and Zn mainly exist in the combined form of ferromanganese oxide.In general,the availability of heavy metals is low and has certain stability;K,Pb and Cd mainly exist in residue form,and the form of heavy metals is relatively stable.According to Pearson correlation analysis of heavy metal speciation and physicochemical properties of electrolytic manganese residue,it is shown that electrical conductivity(EC)and soil organic carbon(SOC)are the main factors affecting the distribution of heavy metal speciation in electrolytic manganese residue.(5)As time goes on,catalase(S-CAT)gradually increased with the prolongation of treatment time,with significant differences among treatments;There was no basic rule among sucrase(S-SC)treatments;Urease(S-UE)gradually decreased with the extension of treatment time,and there was significant difference among different treatments;Alkaline phosphatase(S-AKP)decreased first and then increased.According to the correlation analysis of enzyme activity with physical and chemical properties and heavy metal forms,catalase(S-CAT)was significantly correlated with pH,EC,K,Ca,Cu,Fe;Sucrase(S-SC)was significantly correlated with SOC and K;Urease(S-UE)was significantly correlated with EC,SOC,TN,K,Cu,Fe,Zn;Alkaline phosphatase(S-AKP)was significantly correlated with SOC,TN,Ca,Mn,Cu,Fe,Zn.(6)As time goes on,the α-diversity of each treatment mainly showed a decreasing trend.Through the comparison of time series,there was no significant difference in the dominant bacteria among the treatments,which were Proteobacteria(17.59%～82.22%);Actinobacteria(7.56%～40.27%);Bacteroides(2.38%～29.51%).According to the correlation between microbial community and soil properties and Redundancy(RDA)analysis,the physicochemical properties and enzyme activity of electrolytic manganese residue have a significant impact on the relative abundance of bacteria and bacterial community structure.After 90d,TN(p=0.002)and TP(p=0.011)were the main drivers of bacterial community distribution;At 180d and 360d,SOC(p=0.0005)and TN(p=0.0005)were the main drivers of bacterial community distribution.