Study On Remediation Technology Of Contaminated Site Of Arsenic Plant Site

With the increasing emphasis on soil ecological environment in China,a large number of illegally constructed smelters such as arsenic plants have been banned and closed,but there are many environmental problems such as serious acidification of soil and serious pollution of heavy metals,which need to be repaired.And governance to eliminate or reduce ecological environmental risks.At present,solidified/stabilized(S/S)technology is a hotspot in the research of remediation and treatment of heavy metal contaminated sites.The development of safe and long-lasting curing/stabilizing materials has become the key to this technology,including the metal-containing arsenic(As)multi-metal composite contaminated site soil.The development of S/S materials is particularly urgent.In this paper,the soil of the contaminated site in a arsenic plant in Guangxi is taken as the research object.By consulting the literature,the hydrotalcites with high efficiency and good stability of heavy metals in the removal of water environment are selected as the main S/S materials.The effect of solidified/stabilized materials(CaO,Portland cement,FeCl3,FeSO4)in arsenic-contaminated soils;followed by hydrothermal reaction to prepare magnesium-aluminum hydrotalcites(MgAl-LDHs,UMgAl-LDHs),magnesium-aluminum Iron-type hydrotalcite(MgAlFe-LDHs,UMgAlFe-LDHs),a total of four materials,modified at high temperature(450?)to obtain magnesium-aluminum composite oxide(MgAl-LDO,UMgAl-LDO)and magnesium-aluminum-iron composite oxide(MgAlFe-LDO,UMgAlFe-LDO),a total of eight materials.Four materials of MgAl-LDHs,MgAlFe-LDHs,MgAl-LDO and MgAlFe-LDO were subjected to X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),and thermogravimetry(TG).Analytical,specific surface area and pore analysis(BET)and other material characterization;the effect of hydrotalcite before and after modification on the multi-metal solidification/stabilization of soil in the contaminated sites of the arsenic plant and optimization of application conditions,and the selection of optimal solidified/stabilized materials and application conditions and carry out pilot tests at the site of the arsenic plant to provide a practical basis for the rehabilitation of such sites.The main findings are as follows:1)The characterization results of the prepared and modified materials show that the introduction of Fe3+ into MgAl-LDHs can form MgAlFe-LDHs with well-known hydrotalcite structure diffraction peaks and good crystal form,both of which have huge specific surface area and rich Hydroxyl groups,but compared with the MgAl-LDHs material,the specific surface area of MgAlFe-LDHs increases,the pore structure decreases,the characteristic diffraction peaks and peaks decrease,the diffraction peak shifts,and the crystal structure is slightly poor.The characteristic diffraction peaks of LDHs disappeared in the LDO materials modified by high-temperature calcination,which became the diffraction peaks of magnesium-aluminum oxide conjugates.The layered scale structure disappeared and the mass decreased.-OH and CO32?became H20 and CO2 but the specific surface area Increased,these features help the material repair heavy metals.2)In the study of the repair effect of hydrotalcite-like materials,the addition of F5(FM300),(FM80)and other hydrotalcite-like materials,as a curing/stabilizing material applied to the soil,can significantly increase the soil pH value,for Cd,Zn,Cu,As and other heavy metal composite pollution treatment has significant effect.Under the 3.0%material addition amount,the Cd and Zn repair effects have not fully met the sewage discharge standard and the repair target value,but the soil As can meet the discharge standard and the repair target after treatment.The results,compared with the effect of curing/stabilizing different types of hydrotalcite materials,found that MgAl-LDHs and MgAlFe-LDHs can meet most of the requirements of composite pollution treatment and repair in the arsenic plant,and the effect is better than the purchase.Hydrotalcite-like material.When the addition amount of MgAl-LDHs is 5.0%,the curing/stabilization rate of Cd,Cu and Zn is more than 99%,the As solidification/stabilization rate is about 90%,and the As solidification/stabilization rate reaches the emission standard and target repair.Value,the material effect in the late stage of the experiment has no significant change in pH value,and can be used as an actual repair material.3)The practical application results of MgAl-LDHs material repairing the residual site of the arsenic plant are the same as the laboratory test results.The S/S rate of Cd,Zn and Cu in the aqueous extract and acid extract is over 95%.The As S/S rate is over 90%,and the pH of the material is also improved.After the repair,the heavy metal concentration and the pH value of the soil water extract reach the emission labeling and target repair standards.In the actual repair of the subsequent arsenic plant,this material can be used for the treatment of contaminated sites.