Integrated Use Of Biochar With Unconventional Carbonaceous Amendments For Transformation Of Toxic Metal(loid)s In Soil-plant System

With the increasing mining and industrial development over the last few decades,several anthropogenic activities are responsible for heavy metals(HMs)release in soil which particularly leads to the serious soil and environmental crises.These multi-contaminated soils with poor physico-chemical properties cause several HMs to persist in soil for long time duration due to their minimum chemical and biological reduction which ultimately prevent the plant growth.A number of physical,chemical,and biological remediation techniques have been developed which are helpful to reduce the risk of heavy metals in the agricultural soils,industrial multi-contaminated soil and copper mine tailings.Among them,one remediation technique is in-situ immobilization by using high surface area organic or inorganic sorbent to reduce the bioavailability and mobility of metal cations depending on the soil or copper mine tailing physico-chemical structure as well as the quantity of the HMs released into the environment.Metal immobilization with different organic and inorganic amendments is considered a low cost management practice and an environment friendly which successfully immobilizes metal ions by various chemical and biological reactions mainly through precipitation,adsorption,and complex forming processes.In present study,In-situ stabilization of HMs such as Cr,Co,Ni,Cu,Zn,Cd,and Pb using bamboo-biochar with unconventional carbonaceous amendments such as fly ash,coal gangue,bituminous coal and lignite have been tested as an immobilizing agents for HMs in mine contaminated soil and copper mine tailing.Additionally,coal gangue and bituminous coal were hydrothermally treated and fly ash were acid washed and hydrothermally treated prior to use with biochar.These amendments were applied individually to various ratios(1%and 2%)or combined with biochar according to the experimental designs.The applied amendments,amended soil and copper mine tailing samples were physico-chemically analyzed and characterized to find the HMs leachability,bioavailability,and speciation using several techniques(ICP-AES,ICP-MS,SEM/EDS,XRD,XPS,FTIR,BET,particle size analyzer,and Elemental analyzer)and their uptake,transfer rate(TR),bioconcentration factor(BCF),and translocation factor(TF)to maize,rapeseed,and wheat were determined by crop harvesting.Moreover,the root and shoot samples of plants were analyzed using ICP-MS for HMs contents in plant parts.In case of mine contaminated soil the addition of bamboo-biochar with acid washed fly ash and hydrothermally treated raw fly ash and coal significantly increased the soil pH,EC,and soil organic carbon(SOC)and decreased the bioavailability of Cr,Co,Ni,Cu,Zn,Cd,and Pb in soil compared to the control.In case of copper mine tailing,a high Cu and other HMs concentration in pore water and amended copper mine tailing were reduced by combination of bamboo-biochar with hydrothermally treated coal gangue and lignite.Sequential extractions results showed a reduction in the exchangeable fraction of HMs and elevation in the residual fraction following the addition of biochar either applied alone or in combination with different amendments such as lignite,raw and processed fly ash,coal gangue,and bituminous coal.However,individual application of these carbonaceous amendments were less effective for heavy metals leaching,bioavailability,and metal speciations as compared to the combined with biochar.Meanwhile,combined application of biochar with carbonaceous amendments also stimulated the plant growth by increasing biomass production,roots and shoots elongation as well as higher uptake of macronutrients.Moreover,XRD,XPS and FTIR results of biochar-carbonaceous complex shown the role of hydroxyl,carbonyl,carboxyl,and amide groups based functionalities in HMs immobilization.Thus,these findings indicated that combined application of biochar with carbonaceous amendments is an effective strategy to long-term stability and immobilization of HMs in soils around the coal mines and copper mine tailings and accumulation in plants and as well as improve crop production.