Ecological Risk Assessment On Sediments In Sb-mining Area And Development Of Restoration Technology

Antimony production and reserves in China is the highest in the world. It is one of the most important strategic resources and is widely used in chemical, electronics and pharmaceutical industries. Antimony resources in China are mainly produced in the southern provinces of Hunan, Guizhou, Guangxi etc. Mining, smelting and processing of antimony products have led to serious water contamination in antimony-mining areas. Focused on antimony contaminations in water and sediments in antimony-mining areas, this thesis carries out research work on antimony contamination investigation, biological availability analysis, ecological risk analysis of antimony and other heavy metals, the stability and release risk of antimony in sediments of polluted rivers, absorptive removal from water, and safety assessment on adsorption materials.First, antimony in river water and sediments at downstream rivers from GuangXi Dachang antimony mining areas were investigated.14samples were collected. Antimony in water are from59.1-213.8μg/L, with an average concentration of139.9μg/L. Antimony in sediments are from5.06-20.9mg/kg, with an average concentration of12.9mg/kg. The species of antimony in sediments were analyzed using the Tessier sequential extraction method. The results showed that8.11-75.1%of Sb in sediments were combined to iron oxides and manganese oxides, and3.35-39.2%of antimony in residual,9.87-32.4%associated with carbonate salts,15.5-32.4%in organical-binding form and the other3.10-16.0%in water dissolvable form. In addition, the average concentrations of Cd、Cu、Ni、As、 Zn、Pb and Cr in sediments are10.9mg/kg,204mg/kg,247mg/kg,19.3mg/kg,1329mg/kg,44.0mg/kg and101mg/kg, respectively. In sediments, Cd and Sb, having the largest potential ecological risks, are the major ecological risk factors in this area. The potential ecological risks of the other6metals including Cu, Ni, As, Zn, Pb and Cr are in a descending order. Since Cd contaminations in sediments and water have been intensively reported in recent years, so it is not focused in the further study.To investigate the effect of aquatic chemistry on antimony release from Sb-contained sediments, samples from the down-stream of an antimony-polluted reviver were characterized. Their X-ray diffraction patterns (XRD), Fourier transform infrared spectra (FTIR) and X-ray fluorescence spectra were collected. Moreover, the effect of pH, salty and concentrations of humic acids on the release of antimony were also investigated. The results showed that all sediment samples contained similar mineral phases, surface groups and similar main element contents. Identified phases included quartz. albite, muscovite, calcite and stewartite. Elements at the surface of the sediments followed the order of Si>Al>Fe>Ca>K>Mg>Mn. Batch release experiments showed that the amounts of released antimony increased with decreasing pH, increasing concentrations of salinity and humic acids. pH was the most important factor to affect antimony release.22～153μg/L of antimony was released from the14sediments at conditions of pH3.0±0.2, the adsorbent dose of1g/0.1L, shaking time of3h at160rpm. With increasing concentrations of salty and humic acid, the released antimony ranged from26to180μg/L, and from22to153μg/L, respectively. Among the three investigated factors, the effect of pH was the most intensive one. It is speculated that the release was caused by pH-related mineral dissolution and desorption, and the final states was an equilibrium of the both processes. At pH=3, the released antimony was positively correlated to the contents of Mn at the surface of sediments. That means that dissolution of stewartite rather than surface adsorption markedly affected the release of antimony.The adsorption treatment study is adopted on the antimony-polluted water sample, and Iron-Zirconium Oxide Particle (IZOP) prepared by coprecipitation method can effectively absorb Sb(V) from water. Structure and surface analysis on IZOP shows that the adsorbent particle is micron-sized, amorphous-structured, has large specific surface areas, and the pore volume is0.42ml/g. The test of IZOP’s absorption of Sb (V) shows that the optimum adsorption pH range is neutral partial acid (<7.5), and Sb (V) adsorption process is in line with the pseudo-second order rate equation. Under neutral conditions, the maximum adsorption capacity was78mg/g at an initial Sb(V) concentration of20mg/L. The isotherm of Sb(V) absorption on the IZOP adsorbent can be modeled by the Langmiur equation. Acute toxicity test and mouse polychromatic erythrocytes toxicology test show that the adsorbent is safe by itself, and the depletion materials after processing meet the Toxicity Characteristic Leaching Procedure (TCLP).This study provides basic information on Sb pollution in water and sediments in a downstream revier in Dachang Sb-mining area, as well as the bioavailabitliy, and ecological risk and the remediation method. Besides, it has a positive meaning for promoting the research level of antimony contamination investigation and ecological risk assesment and the development of remediation technology.