Index Properties, Hydraulic Conductivity and Contaminant-Compatibility of CMC-Treated Sodium Activated Calcium Bentonite

Abstract

A typical sodium activated calcium bentonite (SACaB) was treated with carboxymethyl cellulose (CMC) polymer, called CMC-treated SACaB (CMC-SACaB), and it was investigated for its hydraulic conductivity and enhanced chemical compatibility. Index property and hydraulic conductivity tests were conducted on CMC-SACaB and SACaB with deionized water (DIW), heavy metals-laden water, and actual landfill leachate. Lead-zinc mixed (Pb-Zn) solution and hexavalent chromium (Cr(VI)) solution were selected as target heavy metals-laden water, and calcium (Ca) solution was tested for comparison purposes. The hydraulic conductivity (kMFL) was determined via the modified fluid loss (MFL) test. Liquid limit and swell index in DIW, heavy metal-laden water, and Ca solution increased with increasing CMC content. CMC treatment effectively decreased the kMFL of SACaB when exposed to Pb-Zn solutions with a metal concentration of 1 to 20 mmol/L and landfill leachate. An insignificant change in kMFL of CMC-SACaB occurred with exposure to Pb-Zn solutions with metal concentrations of 1 to 10 mmol/L, Cr(VI) and Ca solutions with metal concentration of 1 to 20 mmol/L, and landfill leachate. A slight increase in kMFL of CMC-SACaB was observed when Pb-Zn concentration increased to 20 mmol/L, and such an increment was more noticeable when the CMC content was lower than 10%. In the DIW, the measured kMFL values of CMC-SACaB and SACaB with a given range of void ratio were consistent with those obtained from the flexible-wall permeameter test.

Improving strength and hydraulic characteristics of regional clayey soils using biopolymers

“…CPP-treated clayey soil had the lowest hydraulic conductivity at the curing time considered. [53] also observed a similar trend of a considerable decrease in hydraulic conductivity for CMC stabilized mineral clay (bentonite).…”

A brief introduction to polymers and concepts of polymer modification of bentonite for barrier applications

“…In geoenvironmental engineering CMC is used for the so called “hyperclay” treatment introduced in Di Emidio 44 . This polymer‐enhanced bentonite has been widely investigated in terms of membrane behavior, hydraulic conductivity under aggressive boundary conditions, 45 and wetting‐drying behavior 2 . CMC, like other polymers of natural origin, is used in food industry, cosmetics and in paper production 44 …”

Consolidation Properties of Soil/Modified Bentonite Backfill in Salt Solution

“…However, in China, India and other countries where high-quality sodium bentonite is scarce and calcium bentonite (Ca-bentonite) is relatively abundant; the latter can be used as an alternative material in SB slurry wall construction after proper modification. Recently, some novel modified Ca-bentonites, such as polymer-modified bentonite [4,5], sodiumhexamatephosphate (SHMP)-modified bentonite [6] have been developed as alternative barrier materials in contaminant control. Especially, a sand-modified Ca-bentonite backfill with an optimum SHMP-modified Ca-bentonite content of 20% by weight was manifested to exhibit comparable hydraulic performance to the typical sand-sodium-bentonite backfill commonly with a bentonite content of 1% to 5% by weight [7,8].…”