Masters Theses

Date of Award

5-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

Kevin Robinson

Committee Members

M.M. Ghosh, R.L. Siegrist

Abstract

Recently, destruction of organic contaminants using hydrogen peroxide (H2O2) has been investigated. Peroxidation, as the process is called, may mobilize metals bound to soil thereby increasing the potential of groundwater contamination and exposure to humans. Mobilization of soil-bound Lead (Pb), Zinc (Zn) and Uranium (U) upon peroxidation of soils was investigated in the present study. We evaluated the viability of soil peroxidation as a means of organic contaminant destruction and the concomitant release of soil-bound metals. An alluvial soil with an organic matter (OM) content of ≈ 1.3% (dry weight basis) was used in this study. This soil was digested with H2O2 under controlled conditions to obtain an OM content of 0.4%. The digested soil was utilized to evaluate the effect of peroxidation upon metals bound to the soil mineral component and refractory OM. Both soils were loaded with each metal (30 mg/kg) and treated with 0 to 32 mg H2O2/g soil (0-3% wt./wt.). Additional peroxide tests were conducted utilizing multiple peroxidation treatments and varying peroxide contact times. Pb, Zn and U binding rates (kinetics) and equilibrium information (isotherms) were also investigated. These tests were conducted to gain an understanding of the metal binding system mechanics. Soil peroxidation may change the pH of the system which may result in mobilized metals. The pH was monitored during soil peroxidation and observed pH changes were modeled in subsequent testing with an acid and base. Additional testing with substantial pH changes induced by an acid and base were evaluated for comparison purposes. Zn mobilization was detected in the natural soil at an H2O2 loading ≤10 mg H2O2/g soil. Zn in the digested soil did not mobilize under the peroxide loadings tested indicating that Zn binding to this soil was to unoxidizable soil mineral components or refractory soil OM. Minimal mobilization of Pb and U was observed in either soil upon single H2O2 treatments with concentrations ≥32 mg H2O2/g soil which may denote a similar binding as observed with Zn in the digested soil. Metal mobilization was observed upon multiple peroxidation treatments at H2O2 loadings of 32 mg H2O2/g soil. Upon repeated treatments, decreasing Zn mobilization and continuous Pb mobilization occurred. Additionally, longer H2O2 contact times resulted in increased metal mobilization. The extended contact times may have resulted in increased oxidation of metal binding sites. A slight pH change in the soil was observed upon peroxidation, however this pH change resulted in no mobilized metal indicating that a mechanism other than pH change resulted in the mobilized metal observed during soil peroxidation. A pH change of one and two units below the natural pH of 6.5, resulted

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