Maya A. Trotz

Delivering Sustainable Infrastructure that Supports the Urban Built Environment

Sustainable living will require megacity-level infrastructural support designs and paradigms.

Characterization and Adsorption of Arsenate and Selenite onto Kemiron

Kemiron, a commercially available, porous iron oxide sorbent was evaluated in batch systems for arsenate (As(V)) and selenite (Se(IV)) removal from aqueous solutions as a function of pH, ionic strength, and particle size (< 38 μ m and between 250 and 425 μ m). BET surface area of Kemiron is 39.8 m2/g and Electron dispersive spectroscopy (EDS) studies found Kemiron to be 40.37% iron and 42.25% oxygen by mass. Langmuir isotherms best described the As(V) and Se(IV) removal at pH 7 with maximum adsorption capacity of 82 mg/g and 52 mg/g respectively. As(V) and Se(IV) sorption decreased as pH increased and both anions were unaffected by sodium nitrate (NaNO3) background electrolyte. As(V) sorption was not affected in surface water samples from the Hillsborough River. Batch kinetic models of the experimental data on the 250 to 425 μ m particle size yielded mass transfer coefficients of 0.0008 min−1 and 0.009 min−1 for As(V) and Se(IV) respectively.

Adsorption of arsenic onto Kemiron in a landfill leachate

Samples of Class I landfill of North Central Polk County contained high level of arsenic (As) above 10 µg L−1, the permissible concentration levels in drinking water. By the method of addition, it was determined that the natural leachate samples contained 29 ± 2 µg L−1 of dissolved As and 126 ± 6 µg L−1 of total As. The sorption capacity of Kemiron fell from 85–90% of the initial 5 mg L−1 As(V) concentration in DI water to 40–50% of 1 mg L−1 initial As(V) concentration in the real landfill leachate system. The age of the landfill leachate exerted no significant influence on the sorption density of As(V) onto Kemiron. There were however small changes in the sorption density of As(III) onto Kemiron. The presence of selenite Se(IV) was the main controlling component in terms of the sorption density of the adsorption of As in the synthetic landfill leachate. Ca2+, –N, , and ions exerted no significant impact on the sorption density of As onto Kemiron. The oxidation reduction potential (ORP) and pH were the most influencing elements besides Se(IV) in the sorption of As onto Kemiron. Changes of ORP also produced changes in pH of the solution systems. In the experiment, the maximum As(V) sorption density acquired was 47.5 mg As g−1 Kemiron at the following: ORP of 320–350 mV at pH of 7–8, ORP of 200 mV at pH of 8, or at ORP of −300 or 0 mV and at pH of 11.

Adsorption of Arsenite onto Kemiron

This study investigated the effect of pH and coexisting ions on As(III) adsorption using batch experiment and discovered that pH strongly influenced As(III) adsorption. However, differences in background ionic strengths of 0.001 N NaNO 3 and 0.1 N NaNO 3 had no effect on the sorption trend. The isotherms followed Freundlich model with Kf of 27.91, 35.67, and 43.76 (mg/g)(L/mg)n at pH 6, 7, and 9 respectively. The kinetic studies showed D app values of (6.52 ± 0.024) × 10 -7 cm 2 /s and (6.22 ± 0.043) × 10 -7 cm 2 /s for the 38 μm and 500 to 600 μm particle sizes. The biot numbers of the sorption derived were 1.84 × 10 -2 and 5.89 × 10 -1 respectively. The presence of CO 3 2- had more impact than SO 4 2- ion but the presence of 300 mg/L NH 4 + - N had no significant impact on As(III) adsorption between pH 4 and 8 and so was the presence of 0.1 mg/L Ca 2+ ion between pH 4 and 6.5. However, about 10% loss of the sorption capacity of Kemiron occurred between pH 6.5 and 9 in the presence of Ca 2+ ion. The presence of 5 mg/L Ni(II) and Se(IV) also showed that Se(IV) was a stronger inhibitor of As(III) sorption than Ni(II). Keywords : Arsenite, ground water, Freundlich, diffusion coefficient, Ghana.