A Low-cost alternative to mitigate heavy metal and phosphorous contamination in water

Abstract

Heavy metals and phosphorous are contaminants that may enter surface waters through mining and agricultural activities. As these activities occur in Alaska, it is important to analyze locally available biosorption materials that may be available in Alaska and may reduce costs to current treatment methods. The adsorption of lead (Pb), cadmium (Cd), and phosphorous (P), by sodium hydroxide-treated, Alaskasourced spruce sawdust at 6.5°C, 15°C and 22.5°C was analyzed. Three kinetic models (zero-order, pseudo first-order, and pseudo second-order) were used to analyze the adsorption kinetics and mechanism. The pseudo second-order kinetic model best described the adsorption of Pb, Cd, and P at all three temperatures, and the adsorption mechanism was determined to be driven by chemisorption. Optimal contact time for adsorption was determined for all three temperatures. At 22.5OC, adsorption equilibrium was reached at 3 hr, 1 hr, and 1.5 hr for Pb, Cd, and P, respectively. Adsorption equilibrium at 15OC was reached at 9 hr, 7 hr, and 9 hr for Pb, Cd, and P, respectively. At the lowest temperature, 6.5 OC, adsorption equilibrium was reached at 11 hr, 14 hr, and 12 hr for Pb, Cd, and P, respectively. Adsorption behavior was further evaluated by fitting the Langmuir and Freundlich isotherm models to the adsorption isotherm data. The adsorption behavior of Pb, Cd, and P were found to vary greatly from each other at each analyzed temperature. Pb adsorption favored the Langmuir isotherm, while Cd and P favored the Freundlich isotherm. Further, adsorption of Cd was found to be unfavorable to the spruce sawdust adsorbent. Apart from elucidating the adsorption properties ofspruce sawdust for locally relevant contaminants, the adsorption data trends in this work suggested that the temperature effects on the adsorption of Pb, Cd, and P vary. The effects of decreasing temperature are not equal for the adsorption of these different sorbates, indicating adsorption limitations at decreased temperatures, that may vary with respect to sorbates analyzed in adsorption studies.