Effects of excessive impregnation, magnesium content, and pyrolysis temperature on MgO-coated watermelon rind biochar and its lead removal capacity

Jingzhuo Zhang,Deyi Hou,Zhengtao Shen,Fei Jin,David O'Connor,Shizhen Pan,Yong Sik Ok,Daniel C.W Tsang,Nanthi S Bolan,Daniel S Alessi

doi:10.1016/j.envres.2020.109152

Abstract

MgO-coated watermelon rind biochar (MWRB) is a potentially highly-effective waste-derived material in environmental applications. This research aims to provide valuable insights into the optimization of the production of MWRB for superior environmental performance. It was found that the Mg content of the MWRB could be easily controlled by adjusting the Mg/feedstock mass ratio during excessive impregnation. The BET surface area was found to first increase and then decrease as the Mg content of the MWRB (produced at 600 °C) increased from 1.52% to 10.1%, with an optimal surface area of 293 m2/g observed at 2.51%. Similarly, an optimum pyrolysis temperature of 600 °C was observed in the range of 400–800 °C for a maximum surface area of the MWRB at a fixed Mg/feedstock ratio of 0.48% (resulting in MWRBs with Mg contents of 1.89–2.51%). The Pb removal capacity of the MWRB (produced at 600 °C) increased with increasing Mg content, with a greatest Pb removal capacity of 558 mg/g found for the MWRB with the highest Mg content (10.1%), an improvement of 208% over the 181 mg/g Pb removal capacity of unmodified WRB produced at 600 °C. The Pb removal capacity of the MWRB (produced with 1.89–2.51% Mg) was also discovered to increase from 81.7 mg/g (at 400 °C) to 742 mg/g (at 700 °C), before dropping to 368 mg/g at 800 °C. These findings suggest that the MWRB can be more efficiently utilized in soil and water remediation by optimizing its synthesis conditions.

Highlights

Heavy metals represent a widely distributed environmental concern due to their presence in industrial emissions and consumer products (O'Connor et al, 2018a; Wang et al, 2019c; Zhang et al, 2018a)
The unmodified watermelon rind biochar (WRB) had an Mg content of 0.62%, and the Mg content of the MgO-coated watermelon rind biochar (MWRB) increased from 1.52% to 10.1% by increasing the initial Mg/feedstock ratios (Figure 1)
The observed increasing trend in Mg content was not linear, tailing off at higher Mg/feedstock ratios, it can be seen that the Mg content coated on MWRB is directly proportional to the initial Mg/feedstock mass ratio, and so it can be controlled

Summary

Introduction

Heavy metals represent a widely distributed environmental concern (e.g., in soil and water) due to their presence in industrial emissions and consumer products (O'Connor et al, 2018a; Wang et al, 2019c; Zhang et al, 2018a). Lead (Pb) is a problematic soil and water contaminant worldwide, posing a significant hazard to human health, especially affecting the development of brain and nervous system children (Shen et al, 2018b; Wang et al, 2019b; Zhang et al, 2019). It was estimated in 2013 that 0.6% of the world’s disease and approximately 853000 deaths were caused by Pb pollution (Shi et al, 2019). Biochar is increasingly regarded as a sustainable solution for water and soil remediation (Hou et al, 2018; O'Connor et al, 2018c; Song et al, 2019)

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