Study On Chromium Migration And Transformation Ingroundwater-rock Interface In The Chromium Salt Production Contaminated Sites

In recent years, with the rapid development of the industry involved in chromium and chromium chemicals are widely used, chromium has become one of the severestheavy metal pollutants in the environment. As the missing of chromium slag heap protection measures and chromium leaking in the process of chromate production, chromate production site has become one of the most chromium polluted area in groundwater in China. Chromium compounds entering the groundwater system migrates and transforms in the groundwater-rock interface, influenced by chromium existing forms, groundwater types, groundwater quality, aquifer physicochemical properties and other factors. Studying on chromium transformation and migration in groundwater-rock interface has an important guiding significance for repairing and fixing chromium contaminated groundwater.This study deals with the problem of pollution of chromium slag heap site in chromate production site in Shaanxi province, carrying out a series of batch experiments and column experiments on the physicochemical properties of chromium slag, leaching toxicity and chromium migration and transformation, the results show that:(1) Chromium slag particle size shows an uneven distribution, and the surface become dense by weathering. Chromium exists as Cr(VI)in chromium slag lixivium, about 6.7g chromium(VI) was obtained from 1kg of chromium slag. The lixivium had higher pH value, less affected by the leaching agent pH, the acid leaching agent makes it easier for the Cr(VI) leaching.(2) Chromium(VI) migration mechanism is different in different types of soils, which influenced by the physicochemical properties of the soil medium. The adsorption of chromium(VI) by mild clay, red soil and loess and initial concentration of the solution has certain correlation. Langmuir and Freundlich isotherm equation can simulate chromium(VI) adsorption process in this three kinds of soil properly. The fitting results show that: there are different kinds of adsorption sites on mild clay and red soil surface with different force, while the adsorption behavior of loess is monolayer adsorption; chromium(VI) adsorption by this three kinds of soil accorded with the second-order kinetics equation, illustrated that adsorption processes are dominated by chemical processes.(3) The retention of chromium in soil mainly includes adsorption, complexation and reduction. When the content of chromium is more than 10 times that quality standard for ground water, the retention capacity of chromium(VI) order in this three kinds of soil is : red soil >mild soil > loess. The proportion of residual form of chromium is largest and uneasily to releaseafter chromium entering the soil. While water soluble and exchangeable states is a little. The percent of other forms of chromium is influenced by the content of organic matter, iron, manganese, aluminum oxide and cation exchange capacity etc.(4) When the pH is less than 12, mild soil, red soil and loess have the certain buffer capacity for the chromium solution pH. In addition, addition of organic matter has a significant effect on the sorption of chromium.