Preparation And Characteristics Of A Controlled Release Potassium Permanganate Oxidant

In recent years, along with the rapid economic development,"three wastes"emissions also gives the environment in which they live great threat. Groundwater, asthe rare resources, is polluted seriously. In the groundwater remediation technologies,in situ chemical oxidation （ISCO） occupy an important position. Of the potentialoxidants, potassium permanganate （KMnO₄） is often used because of its ease ofhandling, relatively low cost and less dependent on pH. But it also has manydeficiencies, for example, when KMnO₄is injected to the underground water, it willrapidly react with pollutions, so as not to work for long time. And excess additive canhave toxicity and secondary pollution risk, but less additive will lead to low removalrate. So a molten suspension and cooling （MSC） method was employed for thecontrolled release KMnO₄（CRP） with a paraffin wax as the coating material. Inunderground environment, KMnO₄can be controlled release and in order to improvethe stability and effective transmission of KMnO₄.In this study, paraffin wax was selected as a coating material and matrix forparticulate KMnO₄. MSC method was employed for the controlled release KMnO₄.Preparation conditions, including KMnO₄particles size, ultrasonic treatment time，stirring speed and the ratio of KMnO₄to wax （P/W） were optimized. The resultsshowed that the average volume particle size of13.20μm, ultasonic treatment of10min and stirring speed at150r/min contribute to the most uniform dispersion of theKMnO₄particles in the molten paraffin wax. The KMnO₄loading amount increasedsignificantly along with the increase of the P/W. When P/W is up to1/2, the scanningelectron microscope images showed that the increased amount of KMnO₄caused thecrushed structure of paraffin wax, which resulted in the higher porosity of wax tocontain more KMnO₄. When P/W is up to1/1, the KMnO₄loading amount from284mg/g to517mg/g. However, the loading amount almost reached saturation by601mg/g when P/W increased to2/1.The releasing characteristics of the samples in the distilled water （concludeddifferent pH values, different temperatures and different dissolved oxygenconcentrations）and the KMnO₄residual amount at different radial distance in the sample were examined by the bench scale tests. The results showed that the releasingof KMnO₄could be divided into four periods and stable release took place after40d.Controlled release KMnO₄oxidant with P/W at1/35was used to remove COD in theleachate and82.9%removal efficiency was obtained after120d treatment.It can be seen from the results that the CRP which was mentioned in this paperhave good released properties, the release process is slow and steady. The CRP has agreat capability to resolve the target pollutants. And CRP has almost no risk ofsecondary pollution.