Date of Award

Summer 2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Jay N. Meegoda

Second Advisor

Methi Wecharatana

Third Advisor

Lisa Axe

Fourth Advisor

Dana E. Knox

Fifth Advisor

Hong Li

Abstract

Chromium contaminated soils, besides being recognized for toxic and hazardous hexavalent chromium, contain high iron concentrations. At some sites, concentrations of iron oxide are higher than 30%. Both iron and chromium in soils have recyclable value provided they can be either concentrated in the oxide form or separated as metal. The concentrated oxide can be used as a substitute for the iron ore. The extracted metal can also be recycled in the steel industry. The objective of this study is to study the feasibility of extracting iron and chromium from soils.

Chromium contaminated soils, can be classified into two groups, one with high iron content having magnetic properties, and the other with low content of iron with no magnetic properties. The extraction of iron and chromium in their oxide forms was conducted using magnetic and gravitational separation techniques. The magnetic separation was found to be better than gravitational separation to concentrate iron and chromium from chromium contaminated soils for the experimental setup. However, the iron content in soil could not be concentrated to as high a level as high grade or processed iron ore, 60-70% iron content.

The reduction of iron oxide to metal can be accomplished at high temperature under the reducing environment. The reduction of iron oxide in soil was quite rapid at temperature higher than 1100°C. The solid carbon was used as a reducing agent for the study of reduction in Thermo-Gravimetric Analyzer. The reduction process was found to be controlled by gasification with the activation energy of 45-55 kcal/mol based on the selected kinetic models. The complete reduction required at least 15% of carbon by weight.

The metal agglomeration and separation occurred when sand was added to soils. The substantial percentage of metal, 15-32 %, was separated from GAR and TPR soils mixed with 15-25% of sand and 15% carbon. The LSP soil mixtures yielded metal separation with sand addition above 20%. Phase and viscosity diagrams were used to explain the metal separation and behavior of the slag. Experimental results demonstrated that iron and chromium can be extracted from chromium contaminated soils found in Hudson County, NJ.

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