Effects Of Biochar From Co-pyrolysis Of Attapulgite And Sludge On Ecotoxicity Of Heavy Metals In Soil

Seven kinds of co-pyrolysis biochar with different attapulgite-sludge were prepared by manually configuring different additions of attapulgite from the excess sludge of Qilihe-Anning Sewage Treatment Plant in Lanzhou,Gansu Province,and passivated the soil polluted by heavy metals?taken from the periphery of Baiyin mining area in Gansu Province?.The structure characteristics of biochar,such as TEM,FTIR,nutrient elements leaching and different pH nutrient elements leaching were studied.Afterwards,the effects of heavy metal contaminated soil on the accumulation of heavy metals in maize were investigated by pot experiment,and the ecological toxicity and passivation effect of biochar-attapulgite-sludge co-pyrolysis biochar were evaluated comprehensively.The main conclusions are as follows:At low pyrolysis temperature,attapulgite content significantly affects the retention of biochar elements.The retention of N,P,Mg,Ca and Fe increases with the increase of attapulgite proportion,while the retention of K and Na decreases with the increase of attapulgite proportion.With the increase of attapulgite proportion,the content of N,P,K,Ca,Na,Fe and S in sludge biochar decreased as a whole.Compared with the sludge biochar without attapulgite,the content of N,P,K,Ca,Na,Fe and S decreased by 18.83%,36.57%,36.77%,23.34%,13.48%,46.92%,53.49%and 33.84%,respectively.The Mg content of sludge biochar increased by 35.18%compared with that of sludge biochar without attapulgite.Calcium,sodium,magnesium,iron and phosphorus are easily released from biochar at low pyrolysis temperature.The influence of different pH on the water-soluble N of biochar is very significant,with the increase of pH,the content of water-soluble N tends to decrease;phosphorus in biochar as amorphous and crystalline mineral leads to the release of more phosphorus at lower pH.The influence of different pH on the water-soluble P of B0,B4 and B5 is consistent,and the content of water-soluble P tends to decrease with the increase of pH;NH₄-N released from biochar decreases with the increase of pH.The influence of different pH on water-soluble NH₄-N of B1,B3,B5 and B6 showed consistency.With the increase of pH,the content of water-soluble NH₄-N decreased,and the amount of NO₃-released from all biochars was almost constant in the whole range of pH.The influence of different pH on water-soluble K of B1,B2,B3,B5 and B6 showed consistency,and the content of water-soluble K decreased differently with the increase of pH.The influence of pH on the water-soluble Na of B0,B2,B4 and B6 is consistent,and the water-soluble Na content decreases with the increase of pH;the influence of different pH on the water-soluble Mg content of B0,B1,B3,B5 and B6 is consistent,and the water-soluble Mg content decreases with the increase of pH;the influence of different pH on the water-soluble Ca content of B0,B1,B2,B4 is consistent,and the water-soluble Ca content increases with the increase of pH.The influence of different pH on the content of water-soluble Fe in B0 and B1 is consistent,and the content of water-soluble Fe decreases with the increase of pH.The influence of different pH on the content of water-soluble S in B0,B3 and B4 is consistent,and the content of water-soluble S decreases with the increase of pH.With the increase of attapulgite proportion,the content of water-soluble N,K,Na,Fe and S in sludge biochar decreased by 25.51%,42.67%,36.21%,36.44%and 30.67%respectively compared with B0.The content of water-soluble Mg and Ca in sludge biochar increased by35.18%and 59.65%respectively compared with B0.Except for Pb,there was no correlation between aboveground heavy metal concentration and DPTA extraction status.For aboveground plants,except Cd,there was a significant positive correlation between different heavy metals and TCLP extractable state under different biochar treatments?P<0.05?.The correlation coefficients between heavy metals in different forms and aboveground enrichment of maize were significantly different.Except for Pb,there was no correlation between aboveground heavy metal concentration and DPTA extraction status.For heavy metal enrichment in underground plants,there was a significant correlation between copper enrichment in underground maize and TCLP extraction state?P<0.05?,zinc enrichment in underground maize and TCLP extraction state?P<0.05?,and nickel enrichment in underground maize was significantly correlated with TCLP extraction state?P<0.01?.There was no correlation between cadmium enrichment in underground maize and TCLP extraction state,and lead enrichment in underground maize.There was a significant positive correlation with TCLP extractive state?P<0.001?,and the correlation coefficients between different forms of heavy metals and the enrichment of underground parts of maize were significantly different.Under B2 treatment,the transport coefficient of Cd in maize was the largest,and for Cu,Zn,Ni and Pb,the transport coefficient was the largest under CK treatment.The accumulation of Cd in maize was less than the concentration of Cd in soil,i.e.,the enrichment coefficient was less than 1.For aboveground plants,the enrichment coefficients of Cu,Zn,Ni,Cd and Pb are the largest under CK treatment,while for underground plants,the enrichment coefficients of Cu,Zn,Ni,Cd and Pb are the largest under CK treatment.Adding biochar could alleviate the inhibition of heavy metal contaminated soil on maize seed germination,and the highest germination rate was 88.33%under biochar B3 treatment.After 30 days of pot culture,the aboveground fresh weight,aboveground dry weight,underground fresh weight,underground fresh weight,root length and stem length of maize plants treated with biochar were significantly higher than those of the control group.Different biochar significantly affected the growth indexes of maize.With the increase of the proportion of biochar attapulgite,the growth index of maize plants increased first and then decreased.When adding biochar B3,the plant height and underground fresh weight of maize were the largest;when adding biochar B4,the aboveground fresh weight,aboveground dry weight and root length of maize were the largest;under biochar B2 treatment,the underground dry weight was the largest.Biochar could inhibit the enrichment of heavy metals in maize,and the enrichment of heavy metals in different biochar treatments was significantly different.For heavy metals such as Cu,Zn,Ni,Cd and Pb,adding biochar.