Environmental Impacts and Immobilization Mechanisms of Cadmium, Lead and Zinc in Geotechnical Composites Made from Contaminated Soil and Paper-Ash

Marija Đurić,Primož Oprčkal,Alenka Mauko Pranjić,Radmila Milačič,Vesna Zalar Serjun,Ana Mladenovič,Janez Ščančar

doi:10.3390/app112411822

Abstract

Paper-ash is used for remediation of heavily contaminated soils with metals, but remediation efficiency after longer periods has not been reported. To gain insights into the mechanisms of immobilization of cadmium (Cd), lead (Pb), and znic (Zn), a study was performed in the laboratory experiment in uncontaminated, artificially contaminated, and remediated soils, and these soils treated with sulfate, to mimic conditions in contaminated soil from zinc smelter site. Remediation was performed by mixing contaminated soil with paper-ash to immobilize Cd, Pb, and Zn in the geotechnical composite. Partitioning of Cd, Pb, and Zn was studied over one year in seven-time intervals applying the sequential extraction procedure and complementary X-ray diffraction analyses. This methodological approach enabled us to follow the redistribution of Cd, Pb, and Zn over time, thus, to studying immobilization mechanisms and assessing the remediation efficiency and stability of newly formed mineral phases. Cd, Pb, and Zn were effectively immobilized by precipitation of insoluble hydroxides after the addition of paper-ash and by the carbonization process in insoluble carbonate minerals. After remediation, Cd, Pb, and Zn concentrations in the water-soluble fraction were well below the limiting values for inertness: Cd by 100 times, Pb by 125 times, and Zn by 10 times. Sulfate treatment did not influence the remediation efficiency. Experimental data confirmed the high remediation efficiency and stability of insoluble Cd, Pb, and Zn mineral phases in geotechnical composites.

Highlights

The growth of the human population and activities, like industrialization, mining, and the intensification of agriculture, have made soil pollution one of the world’s most serious environmental problems
The accuracy of the analytical procedures for the determination of the Cd, Pb, and Zn concentrations in extracts from the sequential extraction procedure and the total element concentrations in the soil samples was checked by analyzing the SPS-SW1 Reference material for the measurements of elements in surface waters and certified reference materials
Data from the present investigation based on a sequential extraction procedure and X-ray diffraction (XRD) analyses revealed that paper-ash is an effective additive for the immobilization process in remediation of Cd, Pb, and Zn in contaminated soils

Summary

Introduction

The growth of the human population and activities, like industrialization, mining, and the intensification of agriculture, have made soil pollution one of the world’s most serious environmental problems. It could negatively influence agricultural production, threaten food safety, and endanger the health of natural ecosystems and lifeforms. Heavy metals and metalloids are of great concern due to their potential toxicity, persistency and since they cannot be degraded These elements are frequently released into terrestrial environmental compartments with anthropogenic emissions in the form of soluble, highly mobile chemical species. The most commonly used amendments for in situ immobilization include cement [10], clay minerals [11], zeolites [12], biochar [13], phosphates [14], humic substances [15], and various industrial by-products like fly ash [16], paper-ash [17,18]

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Results

Conclusion