Exploring Potential of Fly Ash–Bentonite Mix as a Liner Material in Waste Containment Systems Under Concept of Sponge City

Abstract

Many studies have been conducted to evaluate fly ash as an additive for the modification of hydraulic properties of soil. However, rarely are studies carried out that quantify physiochemical, strength, and hydraulic properties of fly ash–bentonite mix. Fly ash–bentonite mix may have the potential to be used as a landfill liner material instead of conventional sand in sand-bentonite landfills. Also, with the introduction of the new concept of sponge city, one of the aims of which is to minimize contamination and maximize the use of waste material, the exploration of fly ash–bentonite mix as a cover material in retention systems is highly crucial. The main objective of this study is to explore physicochemical, strength, and hydraulic properties as well as sorption characteristics of fly ash–bentonite mix. The sorption characteristics of the fly ash–bentonite mix for two heavy metals, lead ions (Pb+2) and nickel ions (Ni+2), were investigated. A criterion based on cation exchange capacity (CEC) and specific surface area (SSA) has been proposed. The study also developed correlations for estimating the CEC of soils with SSA and other soil parameters. Hydraulic conductivity decreases approximately four orders of magnitude with an increase in 30 % of bentonite. Unconfined compressive strength (UCS) is found to increase first (up to 40 % fly ash) and then reduces with further increase in fly ash. Furthermore, the curing time is also found to affect UCS significantly. The findings stated that the mix of 70 % or lower fly ash content (in fly ash–bentonite mix) is able to meet standard requirements for hydraulic conductivity and UCS. The Langmuir isotherm is found to better represent sorption behavior of fly ash–expansive soil, with nickel and lead as model contaminants. All the mixes considered in this study exhibited maximum uptake of Pb+2. Sorption decreases very mildly for mixes that have some expansive soil content, whereas it reduces drastically for only fly ash content.

Modelling contaminant transport in fly ash–bentonite composite landfill liner: mechanism of different types of ions

“…It can be observed from Fig. 1a composite having a 30% bentonite and 70% fly ash satisfies the hydraulic conductivity criteria 3 . www.nature.com/scientificreports/ www.nature.com/scientificreports/ depicted in Fig.…”

“…CH). Buragohain et al 3 and Buragohain & Sreedeep 21 have determined the specific surface area and cation exchange capacity of the same materials and these results are also summarized in Table 1. Both bentonite and fly ash majorly comprised of silica and aluminium oxides.…”

“…Other than hydraulic conductivity, strength also needs to be considered in assessing landfill liner material. Earlier studies and environmental guidelines proposed a minimum unconfined compressive strength (UCS) of 0.20 MPa to utilize as a landfill liner material 3 . Few studies reported that waste-bentonite composites satisfy the strength criteria when a correct mix proportion used 3 , 4 .…”

“…Therefore, the curing period prompts an increase in strength and reduction of hydraulic conductivity. Recent studies have examined the amendment of fly ash to the soil, found the enhanced geotechnical properties such as cation exchange capacity, shear strength, and hydraulic conductivity 3 , 7 , 8 .…”

Correlations between physico-chemical properties and nickel adsorption parameters in soils used in sanitary landfill liners

“…Some researchers have determined that characteristics such as organic matter and iron oxides have good correlation with the adsorptive capacity of metals in soil (SILVEIRA et al, 2002), which depends on the variation of pH in the medium (ZHU et al, 2018). Regarding sanitary landfills, recent studies have been developed aiming to improve the behavior of liners and mitigate the negative environmental impacts, such as hydric contamination (MOHAMMED et al, 2016;BURAGOHAIN et al, 2018;BUDIHARDJO, 2018;SOBTI and SINGH 2019).…”