| Waste Residue, Waste Water, Waste Gas are together called as "Three Wastes", they are the main pollutant of all classes of environments. In contrast to Waste Water and Waste Gas, Waste Residue release pollutants through leaching process, which is a complicated water-rock interaction process, and is a hot, also difficult problem in disposition and exploitation of solid waste.The speciality of chrome slag is that the leachate contains Cr (Ⅵ), which is a significant contaminant with high mobility. The output of inorganic salt in our country has occupied the first place in the world, the quantity of chrome slag resulted from this industry gets up to much more than 400 trillion, and it is still increasing at a rate of over 40 trillion per year. The contaminations caused by misconduct of chrome slag, especially the contamination of groundwater, are of common occurrence. So, developping "reaction-transport simulation study of migration of Cr (Ⅵ) in groundwater under the leaching process" will take on important theorical and practical significance.Taking two chrome slag mucks from a large inorganic salt plant in Hubei province as the main research object, through multi-methods, such as field investigation, laboratory tests and numerical modeling together, this paper contrastively analysed the morphology, mineral composition and leaching law of fresh chrome slag and weathered chrome slag, established a reaction-transport model of migration of Cr (Ⅵ) in groundwater under the leaching process, and predicted the translation and hydrogeochemistry process of Cr (Ⅵ) in groundwater.This research combined hydrodynamic dispersion and hydrogeochemical process together, follow a systematic investigation clue of" chrome slag - leaching process - translation modelling - hydrogeochemical process ". It will make important theoretical and practical sense on the scientific management of chrome slag in our country and environmental protection of groundwater.The main researches and results were summarized as follows:(1) The results of water sampling and tests show that, the groundwater in this area are mainly HCO3-Ca type, it was consistent with the local petrographic composition. The groundwater which polluted by chromium was containning Na+ and SO42- with high concentration. The water quality nearby the chrome slag yards was bad, but the hydrochemistry characteristic in the whole area explained that, translation of pollutant was very slow, groundwater in most area outside the plant had not been influenced.(2) The properties of chrome slag had been studied through instrumental analysis methods, such as XRD, SEM+EDX. The results proved: principal mineral composition of chrome slag are larnite (2CaO·SiO2), calcium aluminoferrite (4CaO·Al2O3-Fe2O3), periclase (MgO), brucite (Mg(OH)2), calcite (CaCO3), coesite (SiO2), talc (Mg3Si4O10(OH)2) and little calcium chromate (CaCrO4), picotite ((Mg,Fe)Cr2O4). The fresh chrome slag can be seen with lager grain, rough surface, and many micropore, while the weathered chrome slag can be seen with finer grain, smooth surface, and compact structure. The sodium content of weathered chrome slag was more than fresh chrome slag, this can be explained as that: in company with weathering of external external minerals, the tetrahydrate sodium chromate which present in the inner of crumbs of larnite and calcium aluminoferrite come out gradually, this result is also proving a principle of "brightness reversion" of chrome slag.(3) This research indirectly realized primary process in the rainfall eluviation of chrome slag through a dissolve equilibration experiment of chrome slag. We found that, the digestion of water-solubility Cr (Ⅵ) from chrome slag was a rapid process. After chrome slag dissolved in water, aquation of calcium aluminoferrite, larnite, periclase, calcium chromate or tetrahydrate sodium chromate happened. Particularly, we want to mention about tetrahydrate sodium chromate, though it was unidentificated in phase analysis, according to the composition of leachate which contain Na+, sligh ttetrahydrate sodium chromate must be existed. The digestion equilibrium concentration of Cr (Ⅵ) from fresh chrome slag and weathered chrome slag were both at about 120mg/L, this stated that, the Cr (Ⅵ) leaching rate from old slag were distinctly higher than new slag, it may be caused by that some tetrahydrate sodium chromate crumb liberated from calcium aluminoferrite and larnite by weathering process.(4) Hydro-geochemistry analyses concerning to the leaching process of chrome slag show that: With upgrowth fissures in it, weathering fissure water aquifer was commonly considered as a conductor, but not a continua and stable aquifer. The retention time of leachate in this layer was very short, so we take no account of the reaction in it. While, the sorption of Cr (Ⅵ) by clayey was poor, some organic matter in clayey can reduce Cr (Ⅵ). Therefore, we considered the removal of Cr (Ⅵ) by clayey as a total adsorption process, and through isothermal adsorption experiments, we got out: it was a Freundlich adsorption mode for the absorption of Cr (Ⅵ) by clayey, and the adsorption parameter K was 0.041.(5) Based on the realization of hydro-geological conditions in the area, a conceptual model established: in the plane, the northeast stream boundary was Yangtse River, the southwest impermeable boundary was fault zone of side hill, the northwest and southeast side were generalized as impermeable boundary through considering the ridge line as groundwater divide. With the groundwater direction in the area is from east to west in a whole, so we can set the streamline at terrace along river as impermeable boundary. The Youjia Lake was set as conatant head boundary. The bottom of K-Rdn bedrock which is slightly-weathered, can be seen as impermeable boundary. And set ground surface as a rainfall boundary. In vertical direction, it was been individed to four layers: the first floor was cement floor and man-made impervious layer in the plant side; the second floor is made ground or clayey; the third layer was quaternary eluvium, lacustrine sediments, alluvium and K-Rdn weathering belt; and the fourth layer was K-Rdn bedrock.(6) Visual MODFLOW, a modeling software about three-dimensional groundwater flow and contaminant travel, was used to establish the numerical model. Simulation results show that, as time goes on, migration circle of Cr(Ⅵ) in groundwater becomes larger, but the change is not too much. The most reason is that, the rock and soil in the area have seepage prevention, with a conductivity coefficient less than 10-5cm/s, which have a effect to the retardation of Cr(Ⅵ) translation. On the other hand, with measures through constructing flashing shed, overlay impervious barrier, wastewater reclamation, chrome slag used as reverberatory slag, the pollutant source can be reduced.The pollution plume of Cr (Ⅵ) diffuse to outside plant as groudwater flow. The pollution plume of slag yard in the southwest corner, diffuse as far as Youjia Lake. Cr (Ⅵ) concentration isolines are relatively thick around the major pollution sources in a plane and on the section; and to see on the section, translation depth is larger in the pollution sources. In 2018, the distance of lateral migration will expand to 120m, but changes in the vertical migration distances are small, for 5-10m. In a 30-year-prediction, Cr (Ⅵ) pollution plume in groundwater keeps on moving to Youjia Lake, result in water quality deterioration in Youjia Lake. As there are no well in the pollution plume, it won't influence the quality of digging well and Yangtse Rive.
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