Study On Mechanism And Stabilization Remediation Of High Concentration Of As Contaminated Soils From Gold Mining Area

Soil contaminated by Arsenic （As） is harmful to animals and plants. Taking effectivemeasures to reduce its harm and contaminated soil remediation have become a hot topic inenvironmental science research. In this paper, high concentration of As contaminated soilsamples were taken from a gold mining waste residue area in Qingyuan, Guangdong. Thefly ash, dried sludge, peanut shells, ferrous sulfate and potassium dihydrogen phosphate（KH₂PO₄） were chosen and integrated as stabilizers for stabilization of the contaminatedsoil. Through laboratory test, the effects of adding stabilizers on soil physical and chemicalproperties, morphological changes of As, and leaching concentration of As were analyzed.And a pot experiment was conducted to investigate the effects of different stabilizertreatments on the growth, biomass, aboveground and underground of As contents in Pterisvittata, Vetiveria zizanioides and ramie. Then the stabilization effects of As on contaminatedsoil were analyzed, and the mechanisms of stabilization remediation of As contaminatedsoil were explored. The main results are as follows:（1） The addition of stabilizers could significantly increase soil pH, organic mattercontent, cation exchange capacity. The soil cation exchange capacity had significantpositive correlation with pH and the organic matter content.（2） Concentration of different forms of As in soils were: residue （RES）>Fe-Mnoxide-bound （FeMnOx）>carbonate-bound（CA）>exchangeable （EXC）>organic matter-bound（OM）. Fly ash, dried sludge, peanut shells, ferrous sulfate have good stabilization effect tothe As, make its transformation from the higher activity, migration patterns of strong to lowactivity, high stability of the forms, in which ferrous sulfate had the highest stabilizationeffect. When the addition of10%fly ash,10%dried sludge and1%ferrous sulfate, theconcentration of EXC-As, CA-As, FeMnOx-As, OM-As were significantly reduced, thedecline of62.3%,55.2%,29.6%and58.2%respectively, and RES-As increased by8.1%.While adding KH₂PO₄will activate As in the soil, compared with the control, after adding10%fly ash,10%dried sludge and1%KH₂PO₄, the concentration of EXC-As, CA-As increased significantly, the rate of increase was26.9%,101.9%respectively. In all thecombinations of treatment, added10%fly ash,10%dried sludge,1%peanut shells and1%ferrous sulfate, the oncentration of EXC-As decreased most significantly, the biggest dropof73.3%. Soil pH, organic matter content and cation exchange capacity are the main factorsinfluence the forms of As changes in soil.（3） Fly ash, dried sludge, ferrous sulfate could significantly reduce the leachingconcentration of As. After added10%fly ash,10%dried sludge,1%peanut shells and1%ferrous sulfate, the leaching concentration of As was0.93mg/L, the stabilization efficiencyreached74.8%. While adding KH₂PO₄increased the leaching concentration and mobility ofAs, and the activity effect of KH₂PO₄larger than that the passivation effect of fly ash, driedsludge, peanut shell for As in the soil, and the passivation of ferrous sulfate greater than theactivity effect of KH₂PO₄, but the existence of KH₂PO₄could suppress the ferrous sulfateon the stability of the As. The concentration of EXC-As, CA-As had significant positivecorrelation with the leaching concentration of As in soil, and they were the main factorsaffecting the change of As leaching concentration.（4）The addion of stabilizers on soil remediation could increase plants biomass bydifferent level. Among them, added fly ash, dried sludge and peanut shells treatment, thedry weight of oboveground part of Pteris vittata, ramie increased most significantly,compared with controls increased by4.4times,2.9times, respectively; and added fly ash,dried sludge, peanut shells, ferrous sulfate and KH₂PO₄treatment, the Vetiveria zizanioidesincreased most significantly, increased by14.9times. The content of As in the Pteris vittatawere: aboveground part>underground part, and the content of As in the Vetiveria zizanioides,ramie were: underground part>aboveground part. The addition of fly ash, dried sludge andferrous sulfate could reduce the oboveground content of As in Pteris vittata, Vetiveriazizanioides and ramie, the largest decline of45.5%,29.5%and53.9%respectively. Whileadded fly ash, dried sludge and KH₂PO₄made the oboveground content of As increasedsignificantly in the three plants, a increase of12.8%,25.2%and62.7%respectively.As-accumulate capability of different plants were: Pteris vittata> Vetiveria zizanioides> ramie, tolerance of As: Pteris vittata>ramie>Vetiveria zizanioides. The concentrations ofEXC-As, CA-As in soil were the main factors affecting he change of As content in plants.（5）The addition of stabilizers could increase the amount of plants’accumulation ofAs. In all treatments, with fly ash, dried sludge, peanut shell, ferrous sulfate and KH₂PO₄combination treatment made Pteris vittata, Vetiveria zizanioides and ramie abovegroundaccumulation of As reaches the maximum value, increased by3.7times,12.8times,3.3times, respectively. Stabilizers addition treatment of the high concentration of Ascontaminated soil could not only can reduce the toxicity and migration diffusion of As, butalso could improve the plants growth and increase the accumulation of As in plants, whichcould enhace the ecological restoration of mining areas, and get the removal of As in thecontaminated soil.