Misiones lateritic soil as a safely disposable, single-use adsorbent for arsenate removal

Abstract

Lateritic soil (LS) from Misiones province, Argentina, was evaluated as a single-use, safely disposable adsorbent for pentavalent arsenic (As(V)) removal on three different systems:1) synthetic solutions at [As(V)]0 ≤ 10 mg L-1 and pH 6.5 (LSL); 2) synthetic solutions at [As(V)]0 ≤ 50 mg L-1 and pH 2 (LSH); and 3) three different groundwaters obtained nearby Rafaela city (Santa Fe, Argentina), with [As(V)]0 ≤ 0.165 mg L-1 and 7 < pH < 8 (LSR). Adsorption equilibrium followed the Langmuir isotherm, with qmax= 0.44 mg As g-1 and KL = 51 mg-1 L for LSL, and qmax= 2.1 mg As g-1 and KL = 0.6 mg-1 L mg for LSH. In LSR, an up to 47 times decrease in adsorbed As(V) (qe) was observed, attributable to the presence of interfering ions. Desorption with 0.10 M hydrochloric acid (HCl), acetic acid (HAc) and sodium hydroxide (NaOH) showed that NaOH achieved over 72% As(V) release, while with HAc and HCl was < 10%, indicating near irreversible adsorption. As(V) concentrations in HCl and HAc leachates from LSL and LSR remained below the 1 mg L⁻¹ limit for hazardous waste; for LSH, this limit was surpassed. Kinetic experiments with LSL showed that, after 1 h, desorbed As(V) peaked to 0.2 and 0.07 mg L⁻¹ for HCl and HAc, respectively, followed by gradual re-a, dsorption onto precipitated iron oxy-hydroxides until [As(V)] ≤ 0.06 mg L⁻¹ after 24 h. These results support the suitability of LS as a single-use, safely disposable adsorbent for treating waters with low As(V) concentrations.