Multi-stage Screening Of Biochar And Its Effect On Remediation Of Nickel And Cadmium Contaminated Acidic Soil In Cold Region

The Hongqiling nickel mine in Panshi,Jilin Province has a long history of smelting.The local soil near the smelter has excessive nickel and cadmium,and the soil is obviously acidified,which brings serious risks to the ecosystem safety and human health.Therefore,it is urgent to carry out the remediation research of contaminated soil.In this paper,the adsorption and immobilization of nickel and cadmium on the prepared and modified biochar were systematically studied by solution soil plant three-stage screening technology.The effects of biochar and biochar combined with plant growth promoting bacteria on the absorption,enrichment,transport of nickel and cadmium and resistance to cadmium and nickel toxicity of pakchoi were studied（1）The saturated adsorption capacity of nickel and cadmium on chicken manure derived biochar and mushroom residue derived biochar prepared at 600℃was significantly higher than that on chicken manure derived biochar and mushroom residue derived biochar prepared at 300℃;the preparation temperature had no significant effect on the adsorption capacity of nickel and cadmium on straw biochar.The order of the saturated adsorption capacity of each biochar prepared at 600℃for nickel was:chicken manure derived biochar>mushroom residue derived biochar>straw biochar;the order of the saturated adsorption capacity for cadmium was:mushroom residue derived biochar>chicken manure derived biochar>straw biochar.Eight kinds of biochar were modified,including H₂O₂modified biochar,H₂O₂+K₃PO₄modified biochar,Ca Cl₂modified biochar,alkali magnetic modified biochar,KMn O₄modified biochar,cetyltrimethylammonium bromide modified biochar and Fe-Mn modified biochar;Fe-Mn modified biochar,Ca Cl₂modified biochar,KMn O₄modified biochar and KMn O₄modified biochar It is high adsorption and low desorption biochar.In the co existing solution of nickel and cadmium,the maximum adsorption capacity of biochar for cadmium is higher than that for nickel.Fe-Mn modified and Ca Cl₂modified biochar are less affected by the competitive adsorption of nickel and cadmium.In the compound solution of nickel and cadmium,they can still adsorb nickel and cadmium well.（2）The results showed that the immobilization rates of available nickel and available cadmium were 49.92%-79.03%and 15.43%-53.81%respectively for chicken manure carbon,bacterial chaff carbon,H₂O₂modified chicken manure derived biochar,H₂O₂+K₃PO₄modified chicken manure derived biochar,Ca Cl₂modified mushroom residue derived biochar,alkali magnetic modified chicken manure derived biochar,KMn O₄modified mushroom residue derived biochar,cetyltrimethylammonium bromide modified chicken manure derived biochar and Fe-Mn modified mushroom residue derived biochar.After 10 days of remediation,the fixation rates of available nickel and available cadmium were 79.03%,53.81%,74.63%and 50.52%respectively,and 69.21%and 47.45%respectively.After 10 days of remediation with Ca Cl₂modified mushroom residue derived biochar,the fixation rates of available nickel and available cadmium in nickel soil were72.30%,52.05%,63.73%and 38.74%respectively after 10 cycles of freezing and thawing,and52.61%and 26.20%respectively after acidification.After 10 days of remediation with KMn O₄modified mushroom residue derived biochar,the fixation rates of available nickel and available cadmium were 67.30%,51.10%,63.21%and 37.56%after 10 cycles of freezing and thawing,and51.69%and 25.32%after acidification.The three modified biochars had the highest fixation rates of available nickel and cadmium in soil,and were resistant to freeze-thaw and acidification.（3）The combined effect of biochar and plant growth promoting bacteria was better than the single effect of biochar and plant growth promoting bacteria,and biochar played a major role.The plant height and fresh weight of pakchoi increased by 70.69%～108.64%and 69.72%～100.69%,chlorophyll increased by 5.3～13.3 SPAD,soluble sugar and soluble protein increased by77.63%～112.33%and 84.65%～94.12%,respectively.The combination of Fe-Mn modified bacterial chaff carbon and plant growth promoting bacteria can not only fix a large amount of nickel and cadmium in soil,reduce the accumulation and transportation of nickel and cadmium in soil to pakchoi,but also enhance the ability of cell wall and vacuole to immobilize and retain nickel and cadmium at the cellular level,and make the nickel and cadmium in pakchoi leaves transform from high mobility to low mobility,thus enhancing the resistance of pakchoi to nickel and cadmium The resistance of the plant to antibiotics.The combination effect of Fe-Mn modified mushroom residue derived biochar and plant growth promoting bacteria was the most obvious among the four biochar and plant growth promoting bacteria.Based on the above results,Fe-Mn modified mushroom residue derived biochar can not only adsorb nickel and cadmium well in solution,but also fix a large amount of available nickel and cadmium in soil,and the fixation effect is resistant to freeze-thaw and acidification.In combination with growth promoting bacteria,Fe-Mn modified bacterial chaff carbon can also maximize the transformation of nickel and cadmium from high mobility to low mobility in pakchoi leaves,enhance the ability of cell wall and vacuole to immobilize nickel and cadmium,and reduce the cost In addition,the plant height,fresh weight,chlorophyll,soluble sugar and soluble protein content of Pakchoi increased significantly.The results showed that Fe-Mn modified mushroom residue derived biochar had important practical value in the safe,efficient and sustainable remediation of acid soil polluted by nickel and cadmium in cold region.