Reductive Immobilization of Hexavalent Chromium in Soil Using Hydrazine – Kinetics, Process Optimization, Sonochemical Enhancement, and Cost Estimation

ABSTRACT

The presence of hexavalent chromium in soil poses a grave hazard to the environment and human health. This study explores the effectiveness, mechanism, and economic viability of remediation of Cr(VI)-contaminated soil by hydrazine. Soil-phase batch kinetic experiments were performed to examine the feasibility of reducing Cr(VI) while finding the effects of relevant process parameters, such as initial Cr(VI) concentration, hydrazine dosage, pH, soil-to-water ratio, and temperature. The materials were thoroughly characterized to gain insight into the mechanism. TCLP tests were done to affirm the immobilization stability. Complete Cr(VI) reduction was achieved within 3 h using a moderate 326% excess of hydrazine at neutral pH. Sonication of the soil mixed with hydrazine using a probe-type sonicator accelerated the reduction of Cr(VI) to Cr(III). Kinetic data could be adequately fitted in a second-order rate model, where the rate constant shows a linear dependency on the soil-to-water ratio. Additionally, the logarithmic rate constant demonstrates linearity within the pH range. The leaching toxicity of Cr(VI) and Cr_total complied with the USEPA regulatory limit and remained stable for 75 d. Hydrazine alone and its combination with ultrasound are sustainable and economically feasible for effective remediation of Cr(VI)-contaminated soil. The statistical analysis using RSM indicated a 99.4% reduction, aligning closely with the calculated optimized value. The optimal process conditions are easy to implement for field application at a competitive cost compared to other reductants. A simplified economic analysis was done to check the competitive acceptability of the technique, considering the construction cost of the remediation plant and its daily operational and maintenance expenses. The results show that the proposed technique will be a competitive one for field applications for the remediation of soil contaminated with Cr(VI). The data and kinetic rate equation will be useful for the process design of the remediation of soil contaminated with Cr(VI).

KEYWORDS:

• Cr(VI) reduction
• hydrazine
• toxicity characteristic leaching procedure
• ultrasonication
• optimization of Cr(VI) reduction

Acknowledgments

The authors acknowledge the Department of Chemical Engineering and the School of Environmental Science and Engineering for providing technical support and a research grant.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions statement

Sutanu Maiti: Conceptualization, Investigation, Data curation; Software, Validation, original draft. Sudha Goel: Conceptualization, Resources, Supervision, Funding acquisition. Binay K Dutta: Conceptualization, Methodology, Supervision, review & editing.

Data availability statement

Data will be made available on request.

Supplementary materials

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15320383.2024.2361010