Feasibility study to extract iron and chromium from chromium contaminated soils

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

Remediation and reuse of Chromium contaminated soils through cold top ex-site vitrification

More than 150 sites in Hudson County, New Jersey are identified as chromium contaminated sites. Hexavalent chromium, highly soluble in water, is considered as an environmental and health hazard, classified as a group A human carcinogen. In this research, the feasibility was performed to study the possibility of remediation of chromium contaminated soil by ex-situ vitrification and to evaluate reuse potential of vitrified products as highway construction aggregate. A series of physical and chemical analysis was conducted on nine soil samples collected from different chromium contaminated sites. Results were analyzed for their compatibility for vitrification. Sand and carbon were added to enhance vitrification process. Vitrification was performed and the vitrified products were subjected to further chemical and physical tests. TCLP chromium concentration results verified a successful remediation. The vitrified product properties complied with the New Jersey Department of Transportation standards, designating high reuse potential

Processes of Removing Zinc from Water using Zero-Valent Iron

Zero-valent iron has received considerable attention for its potential application in the removal of heavy metals from water. This paper considers the possibility of removal of zinc ions from water by causing precipitates to form on the surface of iron. The chemical states and the atomic concentrations of solids which have formed on the surface of zero-valent iron as well as the type of the deposited polycrystalline substances have been analyzed with the use of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The BET surface area, the pH at point of zero charge (pH(PZC)), the ORP of the solutions, and the pH and chemical concentrations in the solutions have also been measured. Furthermore, the paper also considers the possibility of release of zinc from the precipitates to demineralised water in changing physicochemical and chemical conditions. In a wide range of pH values, Zn(x)Fe(3 − x)O(4) (where x ≤ 1) was the main compound resulting from the removal of zinc in ionic form from water. In neutral and alkaline conditions, the adsorption occurred as an additional process

Enforcing memory safety with programmable tagged architecture

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 104-112).Buffer overflow is a well-known problem that remains a threat to software security. With the advancement of code-reuse attacks and return-oriented programming (ROP), it becomes problematic to protect a program from being compromised. Several defenses have been developed in an attempt to defeat code-reuse attacks. However, there is still no solution that provides complete protection with low overhead. In this thesis, we improved TAXI, a ROP defense technique that utilizes a tagged architecture to prevent memory violations. Inspired by Programmable Unit for Metadata Processing (PUMP), we modified TAXI so that enforcement policies can be programmed by user-level code and called it P-TAXI (Programmable TAXI). We demonstrated that, by using P-TAXI, we were able to enforce memory safety policies, including return address protection, stack garbage collection, and memory compartmentalization. In addition, we showed that P-TAXI can be used for debugging and taint tracking.by Witchakorn Kamolpornwijit.M. Eng