Study On Controlled Release Materials In Groundwater Remediation

Controlled release materials（CRMs）are emerging oxidant delivery techniques for in-situ chemical oxidation（ISCO）for groundwater remediation.Successful implementation of CRM relies on good understandings of the kinetics and mechanism of controlled release of reactive agents.Four types of controlled release materials,including KMn O₄-paraffin,persulfate-paraffin,KMn O₄-cement and persulfate-cement,were prepared in this paper.Batch experiments and model simulations were conducted to explore the impacts of CRM properties（composition and size）and environmental conditions（temperature,p H,water volume and anions）on oxidant release from four controlled release beads.Experimental results indicated that higher oxidant mass content resulted in shorter release longevities and higher release rate.Larger bead resulted in lower release rate,longer release longevity,and more oxidant released.Higher temperature of release system resulted in higher release rate and shorter release longevity.It’s worth noting that the high temperature will reduce the release efficiency of persulfate-paraffin CRM and improve the release efficiency of KMn O₄-cement CRM.Acidic p H decreased the total mass of oxidant released from KMn O₄-paraffin CRM and did not affect the other three materials,while alkaline p H did not affect oxidant release.The presence of SO₄^2-,CO₃^2-,Cl^-and Br^-,as well as volume of release system,had negligible impacts on oxidant release.Based on the experimental data,a dissolution-diffusion conceptual model was developed.The above experimental observation and the associated controlled release mechanisms can be qualitatively explained by the conceptual model.Finally,a more detailed two-film boundary mathematical model was developed to simulate KMn O₄ release process.Comparison of modeling results with experimental data suggest that the new mathematical model gave well quantitatively predication.Overall,this study shows that properly designed CRM can sustain release for years,thus representing a cost-effective and low-maintenance groundwater remediation technology.Both CRM properties and environmental conditions significantly affect the release kinetics and longevity,therefore these factors should be considered in the design and maintenance of CRM-based ISCO system.