Document Type

Thesis

Date of Award

1-31-1992

Degree Name

Master of Science in Applied Chemistry - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Bozzelli, Joseph W.

Second Advisor

Kebbekus, Barbara B.

Third Advisor

Shaw, Henry

Abstract

Section I. Chromium is a major soil contaminant of industrial sites in New Jersey, as well as in many of the Superfund sites throughout the United States. Removal of chromium by soil/slag washing with low pH sulfuric acid solutions is described. The extraction parameters are acid concentration, contact time, temperature, solvent/soil ratio, and acid type. The effect of two-stage extraction is discussed.

Soil/slag washing with sulfuric acid concentrations of 2% weight:volume (units are g/ml. This concentration is approximately equal to 0.4 N) at 75:1 v:w solvent/soil ratios yielded chromium extraction efficiencies of 95%, but 50% of the soil matrix was dissolved. Residual chromium concentrations up to 4000 ppm were observed from soil/slag originally containing 21,000 ppm Cr. Residual chromium is postulated to consist of immobilized chromium fixed to the soil/slag matrix, whereas all surface adsorbed and free chromium is removed.

A study of kinetics revealed that extraction at 95°C is completed within five minutes. The effect of temperature is such that chromium removal is improved by a factor of almost two when extraction is carried out at boiling temperature rather than at room temperature. At a 75:1 v:w solvent/soil ratio, peak extraction is achieved at a lower concentration than at 25:1 and matrix weight loss is greater. In addition, at 75:1, 95% chromium extraction is achievable, but at 25:1, the maximum chromium removal levels off at 80%. No signifi¬cant difference is detected in the extractive capabilities of the different mineral acids tested: sulfuric, hydrochlor¬ic, and nitric acids. Sulfuric acid is a suitable choice as extractant because of its lower cost and other advantages, such as its reduced corrosivity.

Section II. Chromium is a major soil contaminant of industrial sites in New Jersey, as well as in many of the Superfund sites throughout the United States. Removal of chromium by soil washing of chromium(III) impregnated Kao¬lin, Montmorillonite, and Bentonite clays with low pH acid solutions is described. The extraction parameters studied are acid concentration and kinetics.

Soil washing with sulfuric acid concentrations as high as 3.3% weight:volume (0.67 N) at 75:1 v:w solvent/soil ratios yielded chromium extraction efficiencies between 87 - 99% for the three clay types when extracted for one hour at 95°C. Residual chromium concentrations were 80 ppm for Kao lin, 40 ppm for Montmorillonite, and 500 ppm for Bentonite. Initial chromium concentrations were 650 ppm for Kaolin, 4800 ppm for Montmorillonite, and 17,000 ppm for Bentonite. A study of extraction kinetics showed that the bulk of the chromium extraction at 2% w:v sulfuric acid concentration at 95°C was completed within 20 minutes.

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Chemistry Commons

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