| In the past few years, Cr(â…¥) pollution problem in unsaturated zone has become more and more serious, and Cr(â…¥) will pollution groundwater through the unsaturated zone. This paper studies about vertical transport of Cr(â…¥) in Unsaturated ZoneIn this paper, by adsorption dynamics experimental, isothermal adsorption experiment and the influence factors, completing the Cr(â…¥) in unsaturated zone different characteristics of the soil sample adsorption characteristic research, and in the soil column leaching experiment filter based on mathematical model predicts chromium in unsaturated zone of migration rule. According to the results, Cr(â…¥) in vadose soil samples of the law to conclusions:1When Cr(VI) solution concentration is0.5mg/L, in30min reached balance adsorption, absorption rate was60%. Soil sample adsorption Cr(â…¥) can be divided into two stages:fast adsorption stage and slow adsorption stage. Rapid reaction stage soil on Cr(â…¥) adsorption effect soon, sharply increased, and the slope is very large. Cr(â…¥) can quickly go the surface of the soil sample particles, quickly form surface charge adsorption. Slow reaction stage, the adsorption and desorption speed flat rate, at this stage, along with the reaction time, Cr(â…¥) began to spread into the soil sample particles, and gradually start to happen lattice reaction plays a main role.2According to the soil sample1and2soil Cr(â…¥) adsorption isotherm equations, data and Freundlich equation and Langmuir equation is fitting, can see the isothermal adsorption Freundlich equation and the linear equation are better fitting degree, correlation coefficient achieve significant level (R2>0.9), which reflects Kf adsorption intensity, and can also reflect adsorption capacity, and the soil sample2Kf0.099, soil sample1Kf0.011, visible soil samples of2adsorption capacity significantly greater than1adsorption capacity of the soil sample, the adsorption experiment according with the practice.3Soil sample adsorption Cr(â…¥) by different pH. When pH value in3-6range, soil sample on Cr(â…¥) adsorption capacity with the increase of the pH value and have to fluctuate, but the basic keep in a horizontal value. When pH>6, adsorption fell sharply, when pH value in10or so, only about35%in adsorption rate. In the acidic conditions, Cr(â…¥) mainly Cr2O72-form exists, so bag with gas soil sample on Cr(â…¥) adsorption rate is higher; In a neutral and alkaline conditions, Cr(â…¥) mainly CrO42-Torm existence, so soil sample on Cr(â…¥) adsorption rate fell sharply.4With the rise of temperature, soil sample on Cr(â…¥) adsorption rate increases, the visible absorption of environmental temperature when to Cr(â…¥) adsorption effect is obvious. Soil on Cr(â…¥)adsorption response is a hot chemical reaction process, different environmental temperature, Cr(â…¥) the adsorption quantity of size, adsorption response speed and all affect the adsorption mechanism.5Soil sample of different proportions of organic matter to Cr(â…¥) adsorption enormous influence. The organic material in the process of decomposition, carbon dioxide and produce all kinds of organic acid, and the response of the environment has certain influence on the pH value, is it absorb environment becomes acidic, be helpful for adsorption. The organic material in the decomposition of the wave and the time, make the adsorption temperature rise environment, but also to the adsorption.6Make tracer chlorine ion in the soil column of migration, get conservative ion penetration curve. The experimental results show that:has it been28h chloride pour out; Cl-concentration spikes in56h, the largest concentrations Cmax=0.128mol/L; In the72h, leachate Cl-in concentration decreases, but reduce rate is very slow. Until the148h Cl-concentration in0.003keep mol/L unchanged. Cl-the concentration of the last curve does not maintain strict normal distribution, Cl-concentration rising rate faster, decrease rate is relatively slow, and "bad-tail" phenomenon is quite obvious.With Cr(â…¥) solution through soil column, get Cr(â…¥) penetration curve. The experimental results show that:71h has it been Cr(â…¥) pour out; Cr(â…¥) maximum concentrations arrived in the184th h, the largest concentrations Cmax=0.572ug/mL; In the184h, in landfill leachate Cr(â…¥) concentration slowly decrease, until the470h, Cr(â…¥) concentration keep in0.025mol/L unchanged, can think leaching experiment ends. End of experiment, bag with gas soil sample on Cr(â…¥) the interception rate was95.6%, compared with the adsorption experiment is bigger, this shows that in the natural conditions, due to the soil sample more, when Cr(â…¥) concentration is smaller, Cr(â…¥) can be folded gas adsorption with soil, and adsorption rate is higher.7Using the model simulation when unsaturated zone is30m, when chromium residue pile of shower in a liquid Cr(â…¥) concentration of0.5mg/L, pour out for30years,40years unsaturated zone bottom Cr(â…¥) concentration will be0.072mg/L,0.328mg/L. When chromium residue pile of leaching out liquid concentration for5mg/L, shower drench out ten years for filtrate,20,30years,40years unsaturated zone bottom Cr(â…¥) concentration will be0.72mg/L,3.44mg/L,4.38mg/L,4.75mg/L. |
PDF Full Text Request