黄土性土壤对铬砷的吸附量及其吸附形态

Adsorption amount and forms of Cr and As in Loessial soil

采用室内实验方法研究了黄土性土壤对Cr和As的吸附特性及Cr和As在土壤中的吸附和迁移形态。结果表明:(1)随着加入Cr、As质量浓度的增大,黄土性土壤对Cr和As的吸附量逐渐增大,吸附率下降;在同一质量浓度下,黄土性土壤对As的吸附量明显大于对Cr的吸附量。黄土性土壤对Cr和As的吸附都符合Langmuir模型,利用Langmuir模型计算出黄土性土壤对Cr的最大吸附量为146.2μg?g-1,对As为510.8μg?g-1。(2)在平衡溶液pH值为3.0～7.0范围内,随pH增加,黄土性土壤对Cr和As的吸附量逐渐增加,吸附量在pH值为7.0时达最大,随后pH增大,吸附量明显下降。黄土性土壤中Cr被吸附的主要形态是HCrO4-,迁移形态是CrO42-;土壤中As的吸附形态主要为H2AsO4-,而迁移形态则为HAsO42-。

Cr and As are poisonous chemical elements that existence widely in soils. In recent years a great deal of untreated waste water containing Cr drain directly into environment in industry, at the same time As is also released largely to the soil because of mankind＇s activities, which is amount to 52 000～112 000 t·a^-1 in the world. These cause pollution of soil and water seriously, and affect directly mankind＇s health and existence. The chemical properties of Cr and As are generally all more stable. Cr and As are not easily degraded by the microorganism. They may be enriched gradually in the living things by food chain and are not discharged easily when they enter into water. They exist in form of negative ions basically, so they＇re difficult to be absorbed by aquatic suspension and soil medium, and they permeate and pollute groundwater through the unsaturated zone. Chemical behavior and movable characteristics of Cr and As show remarkable influences with the varieties of environment condition. Adsorption characteristics of loessial soil to Cr and AS must be researched in order to prevent soil pollution from Cr and AS, which result in plants and groundwater pollution. Research results will provide basis for establishing prevention measures from pollution of Cr and As in loess area. Adsorption characters and form and migration forms of loessial soil to Cr and As are studied. The results show that： （1） Along with concentration of Cr and As increasing, adsorption amounts increase, and adsorption rates decrease in loessial soil. At the same concentration, adsorption amount of loessial soil to Cr is bigger than As. Langmuir equation is suitable to describe isotherm adsorption of Cr and As. The maximum adsorption of loessial soil to Cr and AS that is calculated by Langmuir equation are 146.2 μg·g^-1 and 510.8 μg·g^-1 respectively. （2） Within the scopes ofpH of the equilibrium solution is 3.0～7.0, adsorption amount of soil to Cr and AS increase with pH, and adsorption amounts reach to maximum when pH is 7.0, after that adsorption amount decrease obviously. Adsorption of loessial soil to Cr and As are in the from of HCrO4^- and H2ASO4 respectively, and migration forms are CrO4^2- and HAsO4^2- respectively. When preventions and cure paths of water and soil environment pollution are researched in loess region, it must be considered that groundwater is polluted by and As accumulates in soil layer, both are lay particular emphasis on different aspects.