Removal of heavy metals (Cd and Pb) from aqueous solutions by adsorption using synthetic tobermorite prepared from bio-municipal wastes as adsorbent

Abstract

Contamination of waters by discharge of heavy metals such as Lead (Pb), Cadmium (Cd), Zinc (Zn) etc. from various industrial activities poses a great threat to humans, plants and animals, and thus the need for their removal from waste waters. In this work, synthetic tobermorite was prepared using waste soda-lime-silica glass as silica precursor while snail shell ash was used as source of calcium oxide. Several compositions were formulated with varying combination of soda-lime glass and snail shell ash. The bodies were sintered at 950oC in an electric muffle furnace. Analyses such as scanning electron microscopy (SEM/EDS) and Fourier Transform Infra-red Spectroscopy (FT-IR) was used to assess the microstructure and functional groups present in the developed tobermorite. The synthetic tobermorite was further immersed in aqueous solutions containing heavy metals (Pb2+ and Cd2+) whilst parameters such as temperature, contact time, pH, adsorbent dosage, adsorbate concentration were used to assess the performance of the synthetic tobermorite. The results of the morphology shows that the tobermorites possess irregular and spherical shaped grain with coated water films while the EDS shows the presence of Ca and Si with small amount of Al confirming tobermorite while the FT-IR indicates Ca – O – Si and Si – O – Si as main functional groups. The adsorption experiment performed shows the tobermorite is effective in removal of heavy metals (Pb2+ and Cd2+) studied in this work. However, their performance was impaired at increase in temperature above room temperature.

Calcium Silicate Hydrate Cation-Exchanger from Paper Recycling Ash and Waste Container Glass

“…The ranges of batch uptakes of Pb 2+ reported for bespoke (0.08-1.85 mmol g −1 ) [53,74] and waste-derived tobermorites (0.06-2.25 mmol g −1 ) [18,20,22,24,26,41,42,79] are comparable and do not appear to be related to either crystallinity or Al-content (Table 6). The removal of Cd 2+ is generally less extensive than that of Pb 2+ by both bespoke (0.04-1.36 mmol g −1 ) [53,75] and waste-derived tobermorites (0.111-1.52 mmol g −1 ) [18,20,22,24,25,42,79], and is similarly unaffected by structural order and composition. Pb 2+ uptake by TOB-7 appears at the upper end of the reported distribution for tobermorites, and Cd 2+ removal by TOB-7 falls within the middle of the range (Table 6).…”

“…The batch removals of aqueous Pb 2+ , Cd 2+ , and Cs + from single metal ion solutions by TOB-7 are compared with those of other bespoke and waste-derived tobermorites in Table 6 [18,20,22,[24][25][26][27]35,41,42,53,72,[75][76][77][78][79]. The ranges of batch uptakes of Pb 2+ reported for bespoke (0.08-1.85 mmol g −1 ) [53,74] and waste-derived tobermorites (0.06-2.25 mmol g −1 ) [18,20,22,24,26,41,42,79] are comparable and do not appear to be related to either crystallinity or Al-content (Table 6).…”

“…The batch removals of aqueous Pb 2+ , Cd 2+ , and Cs + from single metal ion solutions by TOB-7 are compared with those of other bespoke and waste-derived tobermorites in Table 6 [18,20,22,[24][25][26][27]35,41,42,53,72,[75][76][77][78][79]. The ranges of batch uptakes of Pb 2+ reported for bespoke (0.08-1.85 mmol g −1 ) [53,74] and waste-derived tobermorites (0.06-2.25 mmol g −1 ) [18,20,22,24,26,41,42,79] are comparable and do not appear to be related to either crystallinity or Al-content (Table 6). The removal of Cd 2+ is generally less extensive than that of Pb 2+ by both bespoke (0.04-1.36 mmol g −1 ) [53,75] and waste-derived tobermorites (0.111-1.52 mmol g −1 ) [18,20,22,24,25,42,79], and is similarly unaffected by structural order and composition.…”

“…PRA and WCG-derived tobermorite (this study) 1.78 ± 0.04 0.65 ± 0.06 0.36 ± 0.03 Bespoke tobermorites [75] 1.85 0.945 -Bespoke tobermorites [76] --0.84 Bespoke tobermorites (microwave synthesis) [77] --0.6 Bespoke tobermorites [53] 0.08-0.895 0.04-1.36 -Bespoke tobermorites [72] --0.564-0.572 Container glass-derived tobermorite [18] 1.66 ± 0.05 0.48 ± 0.01 -Sodium silicate and PRA-derived tobermorites [25] -0.63-1.12 -Snail shell ash and waste glass-derived tobermorite [22] 0.060 0.111 -Blast furnace slag-derived tobermorites [27] --0.112-0.587 Asbestos-bearing disaster waste-derived tobermorite [35] --0.31-0.51 Fly ash-derived mesoporous tobermorite [26] 1.287 --Alumina-extracted coal fly ash-derived tobermorite [42] 1.636 0.937 -Alumina-extracted coal fly ash-derived tobermorite [41] 0.850 Cement bypass dust and glass-derived tobermorite [20] 2.25 1.52 -Incineration fly ash-derived tobermorite [78] --0.40 Bottom ash-derived tobermorite/zeolite mixture [79] 0.381 0.196 Coal ash-derived tobermorite/zeolite mixture [24] 1.98 1.31 -Pb 2+ and Cd 2+ ions are rapidly exchanged for labile inter-layer cations within a few hours, and subsequently also replace structural Ca 2+ ions within the tobermorite lattice over a longer timeframe. In this respect, the steady state uptake of divalent cations is usually established between 3 and 10 days [18,20,22,24,26,41,42,53,75,79]. In addition to tobermorite, other common components present in waste-derived hydrothermal products such as calcite and portlandite, undoubtedly contribute to the removal of Pb 2+ and Cd 2+ via the precipitation of solubility-limiting phases [75], and the amorphous calcium (alumino)silicate gel phase may also enhance the overall sorption capacity.…”