Copper adsorption with Pb and Cd in sand-bentonite liners under various pHs. Part II. Effect on adsorption sites.
The project examined the effect of Pb and Cd on Cu adsorption using sand liners containing 0, 5, and 10% sodium bentonite and exposed to metal solutions at three pH levels (3.7, 5.5, and 7.5). Aliquots of 2 g of liner material were exposed in duplicate, for 14 days, to solutions containing Cu alone or Cu with either Pb or Cd. Selective sequential extraction (SSE) was used to quantity the Cu adsorbed by each liner particle adsorption site (exchangeable, carbonate and hydroxide, oxides and residual). The results indicated that two main factors affected liner material behavior in adsorbing Cu, besides Cd and Pb competition: pH either above or below 6.5; liner cation exchange capacity (CEC) greater or equal and greater than the solution cation equivalence. In general, the liner carbonate and hydroxide fractions precipitated the greatest amount of Cu, under all environmental conditions while the exchangeable, oxide and residual adsorbed more or less the same amount. Lead, and to a lesser extent Cd, significantly increase the mobility of Cu, by competing especially for the exchangeable sites. While Cd also competed against Cu for oxide adsorption, Pb competes for calcium and hydroxide precipitation. Lead, and to a lesser extent Cd, competed especially for the exchangeable site where the adsorption is more dynamic, and less for the more permanent adsorption sites, involving precipitation, and electrostatic bonding.
Department of Bioresource Engineering, McGill University, PQ, Canada.
Saleh
S
Kaoser
Suzelle
S
Barrington
Maria
M
Elektorowicz
Li
L
Wang
D000327:Adsorption; D001546:Bentonite / Q000737:chemistry; D002104:Cadmium / Q000737:chemistry / Q000302:isolation & purification*; D003300:Copper / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007854:Lead / Q000737:chemistry / Q000302:isolation & purification*; D012037:Refuse Disposal; D012822:Silicon Dioxide; D012989:Soil Pollutants / Q000302:isolation & purification*
D012989:Soil Pollutants; D002104:Cadmium; D001546:Bentonite; D007854:Lead; D012822:Silicon Dioxide; D003300:Copper