Preparation Of Slow Release Permanganate Gel For Remediation Of TCE

With the development of industry and agriculture,organic pollution in water and soil is becoming serious,especially the Dense non-aqueous Phase Liquid(DNAPL).As a representative DNAPL contaminants,trichloroethylene(TCE)is sustainable in the soil,difficult to degradation and high toxicity etc,which attracts extensive attention by researchers.Potassium permanganate(KMnO4)oxidation is one of the commonly used methods for handling TCE because of its advantages of convenient transportation and storage,simple operation,low price,wide pH range and high oxidation potential(E0 =1.51V).However utilization of oxidant for TCE degradation is relatively low due to the non-selective oxidation when injected or added by solid or liquid KMnO4.In this study,the slow release permanganate gel(SRPG)was prepared based on the silica sol-gel principle.The conditions of SRPG preparation were optimized and the slow release efficiency of KMnO4 from SRPG was studied.The degradation of TCE in water by the slow release permanganate gel and the influencing factors were also investigated.Furthermore,the effects of SRPG on the degradation of TCE in sand column were explored.The preparation conditions of SRPGO were optimized.The experimental results showed that the increase of temperature accelerated the sol-gel process of silica,but the high temperature caused high energy consumption.The gel time of the silica sol with different mass fraction varied with the different water content.KMnO4 as the electrolyte shortened the gel time.pH has the important effect on the gel process and too low or too high pH caused no gel formation.The best preparation conditions of SRPG were as follows: mass fraction of silica sol was 40 wt%,mass fraction of KMnO4 was 13.02 wt ‰ and pH was 5.5.Once the silica gel was formed,the release rate of KMnO4 is not affected by the mass fraction of silica,the mass fraction of KMnO4 and pH.However,with the increasing the amount of slow release gels,the release effect increased.The effect of SRPG on the degradation of TCE in water was also studied.The results showed that the SRPG could not only oxidize TCE efficiently,but also could dechlorinate with a high rate as 94.25%.The efficiency of TCE degradation with SRPG increased with the increase of the mass fraction of potassium permanganate and the decrease of initialconcentration of TCE.In the range of pH 3-9,SRPG has a good effect in the water,and the degradation effect is improved with the decrease of the pH in the water.Compared with pure solid KMnO4,KMnO4 release from SRPG took more time and more effcicent on the degradation of TCE.The removal efficiency of TCE in soil was studied by using SRPG in the sand column.The results showed that the release of SRPG and the degradation of TCE were affected by the velocity of water.The faster the flow rate,the faster the release rate of the slow release gel but the lower the concentration of potassium permanganate.The appropriate flow rate could ensure the continuous release of potassium permanganate and also provided enough time for the reaction of potassium permanganate and TCE to achieve the purpose of complete removal of TCE.SRPG also has a good effect on the degradation of the soil in the plume pollution zone.Due to the non-selective release and preservation of the SRPG,encapsulated-slow release permanganate gel(E-SRPG)was prepared by encapsulating paraffin wax as shell.The experimental results showed that E-SRPG owned selectivity compared with SRPG.E-SRPG with lipophilic paraffin wax as shell could be solved by TCE and then KMnO4 is releasedin water.The adsorption-dissolve-release-degradation process occurred in degradation of TCE by SRPG.The purpose of selective degradation of solution TCE could achieve and the utilization of KMnO4 improved.