Pollution Control On Acid And Heavy Metals Contaminated Farmland Soils In Mining Area By Using Wasted Eggshells

Environmental pollution caused by development and utilization of mineral resources received more and more attentions by society,and heavy metal pollution and soil acidification by acid mine drainage is one of the most serious environment problems.In this study,based on the investigation of soil heavy metal and acidification in paddy soil,we assessed the heavy metal pollution of paddy soil in the area along the Hengshi River in the Dabaoshan mining area of Shaoguan,Guangdong Province.The eggshell was used as the modifier to explore the way of low-cost reduction the bioavalilability of heavy metal through the indoor pot experiment.The main findings are as follows:(1)The soil pH is 4.34-6.49,and the average contents of heavy metals Cu,Zn and Cd exceeded the standard values by 7.52,2.08 and 5.50 times respectively.The contents of heavy metals Pb,Cu and Zn in the soil profiles(0-100cm)showed that the metal content decreased from top to bottom,Ni and Cd contents increased slightly with the depth of soil.The results of heavy metal speciation analysis showed that Pb and Cu were mainly in the form of reducible and residual states.The main forms of Zn,Cr and Ni were residual.The acid extractable Cd accounted for more than half of the total,and it decreased with the increasing depth.(2)Based on the Grade ? of Environmental Quality Standard for Soil of China,the results of single factor pollution and comprehensive pollution index method showed that the average content of heavy metals in all sampling sites(except Taiping River)is heavily polluted,and the contribution of Cu and Cd is the largest,followed by Zn and Pb.The results of the evaluation of potential ecological hazard index showed that most of the sampling spots and regions are highly risky,and Cd had is the largest hazard index followed by Pb.Fox the six regions,Shangba and Wengcheng are polluted most heavily with highest risk exposure.(3)The indoor pot experiments were designed to investigate the effect on soil pH and the passivation of heavy metals Cu,Zn and Cd by waste eggshell.The results showed that the soil pH value were significantly increased,when the concentration of 10 g/kg eggshell was added under the conditions of dry,wetting and flooding,and neutralized after 30 days.It can significantly increase the non-bioavailability heavy metal content in the soil,and Cu,Zn and Cd increased 10.4,3.01,2.2 times,respectively.Otherwise,it can increase the effective calcium in the soil,and improve the effective level of calcium.Overall the concentration of 1 g/kg eggshell was the best for soil heavy metal remediation under flooding conditions.