Effect of a Passivator Synthesized by Wastes of Iron Tailings and Biomass on the Leachability of Cd/Pb and Safety of Pak Choi (Brassica chinensis L.) in Contaminated Soil

Yang Zhou,Lili Li

doi:10.3390/pr9111866

Abstract

Cadmium (Cd) and lead (Pb) carry a high heavy-metal-toxic risk for both animals and plants in soil. In this study, iron-based biochar (T-BC) was prepared by co-pyrolysis using wastes of iron tailings and biomass with urea as the functioning agents. Field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and toxicity-characteristic leaching procedure (TCLP) methods were employed to analyze the physicochemical characteristics of T-BC. Additionally, a pot trial was conducted to examine the effects of T-BC on the physiological characteristics of pak choi (Brassica campestris L.), the availability of heavy metals, and enzyme activities in the soils. The results show that toxic metals have been volatilized by the roasting process and immobilized within T-BC via the formation of stable metal-compounds during the co-pyrolysis process, which satisfies the requirements of a soil passivator. Incubation experiments showed that the DTPA-extractable Cd and Pb in contaminated soils decreased with an increasing amendment rate. Moreover, in the pot experiments, by adding 1% (w/w) T-BC into soils, the soils benefited from its large adsorption, complex precipitation, and immobilization capacity. Approximately 36% Cd and 29% Pb concentrations of edible parts in pak choi were reduced. The amendment proved promising for the stabilization of Cd and Pb in contaminated soils, while providing a strategy for solving the residual waste of tailings and biomass.

Highlights

Since urbanization and industrialization have spread wildly in China in recent decades, the concentration of toxic heavy metals (Cd and Pb) in soil has increased in various regions [1,2,3]
This study aims to: (1) prepare an iron-based biochar amendment from a residue originating from iron-tailings and biomass by the co-pyrolysis method and investigate the release of toxic-elements from T-BC; (2) evaluate the remediation performance of iron-based biochar in Cd and Pb-contaminated soils using pak choi as model plants
Fourier transform infrared spectroscopy (FTIR) spectroscopy (Shimadzu DR-8001) and scanning electron microscopy (SEM) were used for the assessment of surface functional groups and the structural morphology of the T-BC. Soil properties, such as pH, SOC, CEC, EC, available N (A-N), available P (A-P), available K (A-K), and available K (A-Mg) were determined with the method described by Lu [24]

Summary

Introduction

Since urbanization and industrialization have spread wildly in China in recent decades, the concentration of toxic heavy metals (Cd and Pb) in soil has increased in various regions [1,2,3]. In situ immobilization of soil has been developed for the treatment of contaminated soils, a method which is suitable for wide introduction and application [11,12] This technology is designed to reduce the mobility and biological impact of toxic heavy metals (THMS) in soils through the addition of exogenous soil amendments and a series of physical and chemical reactions affecting the speciation of THMS. Major challenges remain unsolved in the field of soil remediation of nano zero-valent iron and synthetic iron oxide These materials have a relatively high cost and can aggregate into large clusters due to their high surface energy and magnetic interaction, which impedes the series of physical and chemical reactions with THMS and reduces their amendment efficiency. There is a need for promising strategies to solve the above defects and reduce material costs

Objectives

Methods

Results