Experimental Study On Removal Of Cr(?) In Heterogeneous Aquifers By Emulsified Oil-compost Compound PRB Technology

the China Geological Survey project "Hydrogeological survey of Shayinghe-guohe basin" Hexavalent chromium is one of the common groundwater pollutants,which has "three effects".People pay more attention to the remediation of hexavalent chromium pollution.Therefore,based on the project "Hydrogeological survey of Shayinghe-guohe basin" of the China Geological Survey project,combined with the real hydrogeological conditions of the shallow groundwater in the field of Suzhou mining area,this paper uses the emulsion oil compost composite PRB Technology to carry out indoor work In the sand tank simulation experiment of removing hexavalent chromium from groundwater,the removal effect of different proportion of emulsified oil and compost,the migration and distribution of emulsified oil in aquifer,the high removal rate of hexavalent chromium maintained by emulsified oil and the influence of heterogeneity of aquifer on the distribution and removal of hexavalent chromium were studied.The main results and conclusions are as follows:(1)According to the experiment of different ratio of emulsified oil and compost,the peak removal rate of hexavalent chromium in the four groups were 0.31 mg /(L×d)(control group)? 0.455 mg /(L×d)(1:10 group),?0.412 mg /(L×d)(1:50 group)and 0.372 mg /(L×d)(1:100 group),respectively.Therefore,the best ratio of compost and emulsified oil is 1:10;(2)According to the sand column experiment of emulsified oil injection into aquifer,under the condition of fine sand column experiment with hydraulic gradient of 3‰,the effective migration distance of emulsified oil injected with 500 ml concentration of 5g / L in fine sand aquifer is at least 45 cm,the average migration speed is 4.34cm/d,and it can be evenly distributed in aquifer.The injection of emulsified oil has little effect on the permeability of fine sand column,and its permeability coefficient only decreases by about 13%,which will not cause serious plugging of aquifer;(3)The results show that the removal rate of Cr(VI)in homogeneous aquifer can reach 97% by injecting 4L,4L,8L and 8L emulsified oil(concentration is 5g / L)at one time,and the removal rate can be maintained for 16 days.The removal rates of hexavalent chromium were 0.84 mg /(L×d)?0.94 mg /(L×d)?0.84 mg /(L×d)and 1.21 mg /(L×d)respectively after each addition of emulsified oil;(4)According to the three-dimensional heterogeneous sandbox experiment under the real environmental conditions(hydraulic gradient of 3 ‰,water temperature of 19 ?),the results show that:The migration velocity of hexavalent chromium in aquifers with different permeability is different.The horizontal diffusion velocity in coarse sand,medium sand and fine sand is 0.054 m/d,0.036 m/d and 0.018 m/d respectively;After 8L emulsified oil of 5g /Lwas injected into the heterogeneous aquifer at one time,the spatial distribution characteristics of the removal effect of hexavalent chromium pollution in the heterogeneous aquifer are as follows: in the coarse sand layer,hexavalent chromium decreased rapidly,in the middle sand layer,the fine sand layer was the slowest,and the removal rates were 10 mg /(L×d),2.13 mg /(L×d),0.89 mg /(L×d),respectively;Under the experimental conditions,the heterogeneity of aquifer will have different degrees of impact on the removal of hexavalent chromium in each sand layer.The removal rate of hexavalent chromium in the whole heterogeneous aquifer is stable at 90% after the 47 th day,which shows that the impact of the heterogeneity of aquifer on the removal of hexavalent chromium is basically eliminated at this time.