Research On Steel Slag Used For Remediation Of Arsenic Contaminated Groundwater As The PRB Filling

Controlling wastewater with steel slag is a kind of resuscitation way to reach the principle of changing waste matters into useful materials, arsenic contaminated groundwater is one of the serious environmental problems in many countries. Based on the idea of developing economic, stable and effective materials and technology of repairing arsenic contaminated groundwater, the resource characteristics and environmental risk of carbon steel slag and stainless steel slag tail were analysed, the optimum conditions of statically removing arsenic were explored, and the stainless steel tail slag’s modification methods and conditions were studied. Finally the methods and optimum conditions of the regeneration of steel slag were explored by using the simulated dynamic column to control the arsenic contaminated water. The results are summarized as follows:(1) The carbon steel slag and stainless steel tail are mainly composed of Ca, Si, Fe, Mg, Al, and their mineral composition mainly contain magnetite, tricalcium silicate, dicalcium silicate, and iron ore, which can be used for good flocculation, filter and adsorption materials because of their loose porosity and large specific surface area. And the results of leaching-out toxicity test show that the leaching solution’s acidity and alkali, the concentration of fluorine and heavy metal are far less than those of standard’s limits. So there are very low risks of leaching pollution in the environment.(2) The experiment of statically removing arsenic show that the adsorption of arsenic by carbon steel slag is more effective than that by stainless steel tail slag. There are many factors that have significant influence on the effect of removing arsenic by steel slag, such as the grain size and the quantity of steel slag, the pH value of the waste water, the speed and time of stirring, and the initial concentration of arsenic. To the two kinds of steel slag, the effect of removing arsenic in conditions when the initial concentration of wastewater0.2mg/L, the particle size of steel slag20-100mesh, the liquid-solid ratio50:1, weakly alkaline, stirring time30min and stirring speed160r/min is best. The adsorption dynamic rules of arsenic by two kinds of steel slag both meet the second-order Lagergren equation and the adsorption process follows the Langmuir isothermal formula and the Freundlich isothermal formula.(3) The modified method of FeCl3leaching is best. We chose0.5mol/L FeCl3as stainless steel tail slag modifier, the best modification liquid-solid ratio is10:1and modification time is12hours. The optimum conditions of statically removing arsenic are the initial concentration of waste water0.2mg/L, the liquid-solid ratio50:1, weakly alkaline, stirring time30min, stirring speed160r/min. The adsorption dynamic rules of arsenic by stainless steel tail slag which modified by iron meets the second-order Lagergren equation and the adsorption process follows the Langmuir isothermal formula and the Freundlich isothermal formula. Through analyzing the phase and surface topography, it is found that the mechanism that the removal of arsenic is the significantly increased iron oxide and the ducts of the modified stainless steel slag are more unobstructed than parent those, which could effectively increase the specific surface area.(4) The steel slag PRB simulation experiment illustrates that we need to control the initial concentration of arsenic when waste water velocity is fixed, and the hydraulic retention time is the main factor to remove arsenic when the initial concentration of arsenic is fixed. Putting the steel slag PRB into practice shows that the effect of the polluted water treatment by two kinds of steel slag PRB is similar to the early operation period, but carbon steel slag PRB treatment is better.There is more wastewater, the much better carbon steel slag PRB treatment is. However, dealing with6L water, the removal rate is still at around90%, and the effluent water meets the requirement. Therefore, the effect of the two kinds of steel slag PRB are both good.(5) The performance of removing arsenic is significantly improved by carbon steel slag and stainless steel tail slag with iron modification after high temperature burning and regeneration. When the temperature is300℃and the regeneration time is60min, the effect of removing arsenic is equal to the prior. The results of regeneration times test shows that, after four cycles of reuse and regeneration, the arsenic removal by carbon steel slag and iron modified stainless steel tail slag still could reach above90%, which fully shows the two kinds of steel slag which regenerated still have strong ability of removing arsenic, stable performance, and could be used for materials of PRB which could remove arsenic of groundwater long term.