Effects of modification and co-aging with soils on Cd(II) adsorption behaviors and quantitative mechanisms by biochar.

Zhuowen Meng,Shuang Huang,Zhongbing Lin

doi:10.1007/s11356-022-18637-w

Abstract

In this study, original and two KMnO4-modified rice straw biochars (pre- and postmodification) were prepared, which were all pyrolysed at 400°C. Premodified biochar had the largest Cd adsorption capacity, strongest acid and solute buffering capacity, which benefited from the increase of carbonate content, specific surface area, and the emergence of Mn(II) and MnOx through modification. Original and premodified biochars were then conducted four types of aging process by an improved three-layer mesh method, namely, aging without soil and co-aging with acid (pH = 5.00), neutral (pH = 7.00), and alkaline (pH = 8.30) soils. The adsorption capacities of modified biochar were always larger than those of original biochar after aging processes. After four aging processes, Cd(II) adsorption capacities were basically in the order of aged biochar without soil > biochar co-aged with alkaline soil > biochar co-aged with neutral soil > biochar co-aged with acid soil, and KMnO4-modified biochar was always better than original biochar after co-aging with soils. The dominant adsorption mechanism of original and premodified biochars (fresh and aged) for Cd(II) was all the precipitation and adsorption with minerals (accounted for 58.55 ~ 85.55%). In this study, we highlighted that biochar remediation for Cd should be evaluated by co-aging with soil instead of aging without soil participation.

Highlights

In recent years, farmland soils have been seriously polluted by heavy metals from exhaust gas emissions, mining and smelting, of which cadmium (Cd) is recognized as one of the most dangerous heavy metals due to its high toxicity and fluidity; more seriously, it can be enriched in fruits, vegetables, aquatic organisms and eventually enter the human body through food chain, causing kidney failure and other diseases (Chen et al, 2008; Li et al, 2010; Liu et al, 2010; Rizwan et al, 2016)
Premodified biochar had the largest Cd adsorption capacity, strongest acid and solute buffering capacity, which benefited from the increase of carbonate content, specific surface area and the emergence of Mn(II) and MnOx through modification
Cd(II) adsorption capacities were basically in the order of aged biochar without soil > biochar co-aged with alkaline soil > biochar co-aged with neutral soil > biochar co-aged with acid soil, and KMnO4-modified biochar was always better than original biochar after co-aging with soils

Summary

Introduction

Farmland soils have been seriously polluted by heavy metals from exhaust gas emissions, mining and smelting, of which cadmium (Cd) is recognized as one of the most dangerous heavy metals due to its high toxicity and fluidity; more seriously, it can be enriched in fruits, vegetables, aquatic organisms and eventually enter the human body through food chain, causing kidney failure and other diseases (Chen et al, 2008; Li et al, 2010; Liu et al, 2010; Rizwan et al, 2016). It is difficult to produce biochar pyrolyzed at relatively high temperatures (i.e. 500~700°C) under large-scale factory conditions, but Cd(II) adsorption capacities of original biochars pyrolyzed at relatively low temperatures were limited (Han et al, 2013b; Liu & Fan, 2018). To realize the large-scale application of biochar in the field, researches of modified biochars pyrolyzed at relatively low temperature (i.e. 300~400°C) should be increasingly carried out (Wang et al, 2017). As a relatively inexpensive reagent, KMnO4 has been increasingly applied to modify biochars in recent years, and the maximum Cd(II) adsorption capacities of KMnO4-modified biochars were 2.16~5.9 times original ones (Li et al, 2017; Liang et al, 2017; Wang et al, 2015a; Yin et al, 2019)

Methods

Results

Conclusion