Zeolite and high carbon fly ash mixes as liner materials for lead/phenol sorption

Yuan, Guobing (1997) Zeolite and high carbon fly ash mixes as liner materials for lead/phenol sorption. Masters thesis, Memorial University of Newfoundland.

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Abstract

Two natural zeolites, i.e. chabazite (CHB) and clinoptilolite (CLN), and two coal fly ashes, i.e. Lambton fly ash (LBash) and Nova Scotia fly ash (NSash), were studied toward their suitability as construction materials for landfill liners. Lead (Pb²⁺) and phenol (C₆H₅OH) were chosen to represent inorganic and organic leachates. The research was focused on (1) the sorption capacity of zeolite and fly ash against Pb²⁺ and phenol; (2) the hydraulic conductivity of these candidate materials when percolated with aqueous solutions of Pb²⁺ (2500 mg/l), phenol (55 mg/l), and Pb²⁺/phenol mixture (Pb²⁺ = 2500 mg/l and phenol = 55 mg/l), respectively; (3) the interaction among zeolite, fly ash, Pb²⁺, and phenol; (4) the optimum mix design for zeolite and fly ash in terms of leachate retention and hydraulic performance. -- Material characterization revealed that LBash is distinguished from NSash by its unburnt carbon content and surface functional groups. For zeolites, CHB has a higher chemical activity and larger cation exchange capacity than CLN. Batch tests on the four materials demonstrated that CHB was most powerful in Pb²⁺ sorption (210 mg/g) while LBash was most effective in phenol removal (1.3 mg/g). Experimental preference was then given to CHB, LBash, and their mixes. -- During column leaching tests, Pb²⁺ sorption took place on LBash and CHB solids through physisorption, chemisorption, complexation, precipitation, and ionic sieving of CHB micro-pores. Phenol was attenuated by LBash and CHB via acid-base reaction, dipole attraction, and hydrogen bonding. In CHB and LBash mixes, CHB was the principal sorbent with Pb²⁺, while LBash was mainly responsible for phenol retention. When Pb²⁺ and phenol coexist in the system, they compete for all sorption sites except for the CHB micro-pores, which cannot accommodate the size of phenol molecules. The hydraulic conductivity values of CHB and LBash with Pb²⁺ or phenol permeant ranged between 1.7 x 10⁻⁸ and 7.0 x 10⁸ m/s. Mixes of CHB and LBash are less permeable due to a better filling of pore space. Although the three leachates used as permeant had different chemical properties, they were not concentrated enough to alter the hydraulic conductivity of test specimens. -- It was concluded that, under present experimental conditions, a CHB/LBash ratio of 1:1 in weight appeared to be the optimum mix for a liner material which will exhibit a maximum overall retardation of Pb²⁺ and phenol. The 1:1 mixture compacted under standard condition also showed a minimum hydraulic conductivity in the order of 3.0 x 10⁻⁹ m/s.

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