Evaluating the effects of formation and stabilization of opal/sand aggregates with organic matter amendments

Weilun Li; Yilin Wang; Feng Zhu; Xiaobin Li; Qiusheng Zhou; Guihua Liu; Zhihong Peng; Tiangui Qi; Leiting Shen

doi:10.1016/j.jenvman.2023.117749

Evaluating the effects of formation and stabilization of opal/sand aggregates with organic matter amendments

J Environ Manage. 2023 Jul 1:337:117749. doi: 10.1016/j.jenvman.2023.117749. Epub 2023 Mar 20.

Authors

Weilun Li¹, Yilin Wang², Feng Zhu³, Xiaobin Li¹, Qiusheng Zhou¹, Guihua Liu¹, Zhihong Peng¹, Tiangui Qi¹, Leiting Shen¹

Affiliations

¹ School of Metallurgy and Environment, Central South University, Changsha, 410083, China.
² School of Metallurgy and Environment, Central South University, Changsha, 410083, China. Electronic address: wangyilin@csu.edu.cn.
³ School of Metallurgy and Environment, Central South University, Changsha, 410083, China. Electronic address: zhufeng1990@csu.edu.cn.

PMID: 36940603
DOI: 10.1016/j.jenvman.2023.117749

Abstract

Opal (SiO₂·nH₂O, amorphous silica), the by-product of alumina extraction from coal fly ash (CFA), has a strong adsorption capacity and is also an important component of clay minerals in soils. The combining of opal with sand to form artificial soils is an effective disposal strategy for large-scale CFA stockpiles and reduction of environmental risk. Nevertheless, its poor physical condition limits plant growth. Organic matter (OM) amendments have broad potential applications for water-holding and improving soil aggregation. Effects of OMs (vermicompost (VC), bagasse (BA), biochar (BC) and humic acid (HA)) on the formation, stability and pore characteristics of opal/sand aggregates were evaluated through 60-day laboratory incubation experiments. Results demonstrated that four OMs could reduce pH, with BC having the most significant effect, VC significantly increasing the electrical conductivity (EC) and TOC content of the aggregates. Except for HA, other OMs could improve the aggregates' water-holding capacity. The mean weight diameter (MWD) and percentage of >0.25 mm aggregates (R_0.25) of BA-treated aggregates were the largest, and BA had the most noticeable contribution to macro-aggregate's formation. The best aggregate stability was obtained with HA treatment, meanwhile the percentage of aggregate destruction (PAD_0.25) decreased with the addition of HA. After amendments, the proportion of organic functional groups increased, which favored aggregate's formation and stability; the surface pore characteristics were improved, with the porosity ranging from 70% to 75%, reaching the level of well-structured soil. Overall, the addition of VC and HA can effectively promote aggregates' formation and stabilization. This research may play a key role in converting CFA or opal into artificial soil. The combining of opal with sand to form artificial soil will not only solve the environmental problems caused by large-scale CFA stockpiles but will also enable the comprehensive utilization of siliceous materials in agriculture.

Keywords: Aggregate stability; Opal; Opal/sand aggregates; Organic matter amendments; Pore characteristics.

MeSH terms

Sand*
Silicon Dioxide*
Soil / chemistry
Water

Substances

Sand
Silicon Dioxide
biochar
Soil
Water