Study Of Combined Hydroxyapatite/hydrated Calcium Silicate And Biochar Amendment On Typical Heavy Metal Contaminated Soil

Hydroxyapatite/hydrated calcium silicate(HAP/C-S-H)and biochar have been proven to be effective materials for im mobilizing heavy metals.In the pervious research,HAP/C-S-H will bring too much soluble phosphate to the soil environment,leading to excess P and causing eutrophication,which caused second ary pollution.So it is necessary to reduce the amount of HAP/C-S-H.In the present work,HAP/C-S-H-biochar combinations with different ratios was used for the remediation of both single(Cd)and multi-metal-contaminated soil(Pb,Cu,Cd,Zn)remediation with different physicochemical properties.The main contents of this study include:collect the soil form the Yunyuan base of Hunan Agricultural University and add different proportions of HAP/C-S-H-biochar mixtures to soil.A pot experiment was conducted to analyze the effects of various proportions of remediation agents on physic-chemical properties,metal availability and toxicity,enzyme activity and microbial community of two kinds of contaminated soil.The result as follows :(1)The results showed that applying all amendment combinations into soil increased gradually soil p H and available phosphorus as the HAP/C-S-H percentage rose in HAP/C-S-H-biochar combinations.Water-soluble organic carbon(WSOC)of two soils increased as the proportion of biochar increased.The higher p H of two soils was obtained in a certain HAP/C-S-H addition(60%)and biochar addition(40%)(H4B6)in combinations.(2)Due to the increase of p H,the availability of heavy metals in the two contaminated soils significantly reduced.After 152 days,the availability of metal Cd in the single contaminated soil was the lowest.And the availability of metal Cd in various organs of rice cadmium in a single contaminated soil was significantly reduced.In the compound contaminated soil,the bioavailability of Pb and Cu was significantly reduced after adding H4B6.However,it has little effect on th e bioavailability of Zn and Cd.(3)Moreover,amendments can decrease weak acid extraction significantly,and the weak acid extraction of heavy metals decreased gradually with increase of HAP/C-S-H content.Amendments could promote transformation of heavy metals from weak acid extraction to oxidizable fractions and residual fractions,reduced heavy metal toxicity in contaminated soil.(4)At the same time,the availability of heavy metals reduced and soil enzyme activity enhanced as the p H increased,thereby promoting the metabolism of microorganisms in the soil envir onment.(5)The analysis results by high-energy sequencing technology showe d that the addition of two remediation agents can increase the community diversity,species abundance and structural composition after HAP/C-S-H-biochar amendments in soil.(6)In addition,the results of RDA analysis showed that the effective Cu,Cd,Pb,and Zn contents in the soil had an adverse effect on the bacterial community.And increasing the p H of the soil was conducive to the fixation of heavy metal ions,thereby promoting the growth of microorganisms.These results indicate that HAP/C-S-H and biochar can effectively remediate both single and multi-metal-contaminated soil when the addition ratio is 4: 6.