| Chromium slag is the solid wastes generated in the process of producing chromium salt andferroalloy, of which the main harmful component is the hexavalent chromium[C（rVI）]in solublesodium chromate and acid soluble calcium chromate. The leachate stacked for a long timecontains Cr(VI), which is an important pollutant with high mobility. If chromium slag is stacked,not treated, it will infiltrate into underground with rain, snow and surface water, polluting thesurrounding surface water, groundwater and soil seriously.Based on the focus of severe environmental pollution caused by chromium slag mucks andleachate, taking two chromium slag mucks respectively from Shenyang and Jinzhou as treatmentobjects, through indoor experiments, theory analysis, numerical simulation and application,studying with deep level, multidisciplinary, multi-angle, draw the following conclusions:（1）The static soaking-leaching and dynamic leaching experiment on Shenyang andJinzhou chromium slag, measuring the impact of solid-liquid ratio, pH of leaching agent,leaching time, stirring intensity, particle size, temperature on pollutant releasing in chromiumslag, which indicate the mechanism of pollutant precipitation and releasing in different regions.The result shows that chromium slag from Jinzhou has a very high concentration, descendingspeed initially. As time goes on, the velocity becomes lower with Cr(VI) leaking, leadingpollution to soil and groundwater; while chromium slag from Shenyang, the same quality withthe former, has a lower concentration, slower concentration decreasing and descending speed.This all indicates chromium slag from Shenyang has a lighter pollute level, but lasts a longertime.（2）By experiment of static adsorption to leachate using different soils(silty sand, siltyclay), measuring the impact of shaking time, pollutant concentration, pH value, temperature onadsorption to Cr(VI) by silty sand and silty clay, obtaining nonlinear isotherm model; buildingadsorption kinetic equation. The conclusion obtained is that: the law of adsorption can beexpressed as Langmuir, Freundlich and Temkin equations, among which Langmuir is the best; interms of adsorption kinetics, the order of fitting degree is: Elovich equation is the best followedby two-constant rate equation and parabola diffusion worst. Silty clay is better than silty sand infitting degree, reflecting silty clay has a better adsorption property.（3）The laboratory column one dimensional dynamic simulating experiment reveals themigration law of leachate through pollution and pure leaching in soils-groundwater systems. The research shows that: Cr(VI) can be detected after a certain time; the concentration experiences agradually increasing until the peak comes, reaching stable. As the pure leaching goes on, theCr(VI) concentration in the leachate has a tendency of decreasing. Convection, dispersion andadsorption are the main causes for Cr(VI) migration while dissolution plays the most importantrole in pure leaching. The Cr(VI) takes different time to reach zero value. In the research, siltyclay needs a longer time.（4）Chromium slag seeps through the self-made flask model of two-dimensionalheterogeneous aquifer that stores simulation soil of Jinzhou, which reveals the law of leachatemigration in the soil-groundwater system dynamically. The results indicate that: in the horizontaldirection, the concentration peak comes early near the flask upstream and the time is related tothe distance of the pollution sources, the further away from pollution sources, the time longer; inthe vertical direction, the pollution area enlarges continuously with the passage of time. The firstfloor made of silty clay has worse permeability, slower horizontal migration, obvious verticalmigration; the second floor made of sand has better permeability. In this layer, pollutant migratesfaster, in which the convection of underground water plays an important role; the third floor isgravel, in which pollutant migration manifested as convection. The Cr(VI) has good migratoryaptitude as a whole, so pollution can diffuse easily in a short time.（5）Based on the theory of seepage field and concentration field, build three-dimensionaldynamic coupled numerical model under the consideration of advection-dispersion,adsorption-desorption and source and sink and predict pollutant migration and distribution bysimulating chromium slag mucks respectively from Jinzhou and Shenyang. The results indicatethat: the muck from Jinzhou migrates faster, in another word, it can lead to groundwaterpollution several kilometers around in twenty years. If seepage measures have been taken,groundwater pollution can be controlled to some extent, resulting in pollution concentrationdecreasing in monitoring wells; the formation of chromium slag muck from Shenyang is clay, sothe migration rate is slow. It only pollutes the groundwater in the factory in twenty years. |
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