Review on stabilization/solidification methods and mechanism of heavy metals based on OPC-based binders

• Published in: Journal of environmental management 2023-04, Vol.332, p.117362-117362, Article 117362
• Main Authors: Chen, Liyuan, Nakamura, Kimihito, Hama, Takehide
• Format: Article
• Language: English
• Subjects: Calcium; Coal Ash; CSH gels; Immobilization; Industrial Waste; Industrial wastes; Metals, Heavy - chemistry; Soil
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2023.117362

Stabilization/solidification (S/S) with ordinary portland cement (OPC)-based binders is a suitable method to remediate heavy metal (HM)-contaminated soil and reuse resources of industrial wastes. In industrial wastes, alkaline wastes such as red mud (RM), soda residue (SR), pulverized fly ash (PFA), and alkalinity granulated blast furnace slag (GGBS) can immobilize HM ions (Pb2+, Zn2+, Cd2+, Cr3+, and Cu2+) by precipitation. However, some HM ions (such as AsO43−) would redissolve within the strong alkali environment. In this case, PFA, GGBS, metakaolin (MK), and incinerated sewage sludge ash (ISSA) which have low pH, can be used to immobilize HM ions or added to the OPC-based binders to adjust the pH in the soil products. Moreover, the calcium silicate hydrate (CSH), calcium aluminum silicate hydrate (CASH), ettringite (AFt), and calcium monosulfoalumiante hydrates (AFm) generated during the pozzolanic reaction can also immobilize HM ions by adsorption on the surface, ion exchange, and encapsulation. SR and GGBS can be used to immobilize the HMs (such as CrO42− and AsO43−), which are mainly affected by AFt and AFm. For those not affected by AFt and AFm but related to immobilization by precipitating (such as Mn2+), other wastes except SR and GGBS are suitable for treating contaminated soil. Nevertheless, the formation of AFt is also instrumental for soil product strength. There are several factors affecting soil product strength. In the future, the influence of different hydration products on the S/S effects, competitive adsorption of HM ions, effects on long-term HM stabilization, and novel materials are worth being explored by researchers. [Display omitted] •Using wastes instead of OPC can reduce the production of CO2.•Selecting appropriate OPC-based binders to immobilize heavy metals is necessary.•Various pozzolanic products can immobilize different heavy metal ions.•There are several factors affecting the strength of soil products.