Cobalt, Cadmium, and Lead Sorption to Hydrous Iron Oxide: Residence Time Effect

Abstract

The adsorption‐desorption of the divalent metal cations (Me2+) Co2+, Cd2+, and Pb2+ to hydrous ferric oxide (HFO) was investigated as a function of oxide aging and Me2+‐oxide residence time. The HFO was produced and stored for up to 86 wk. Periodically, Me2+ sorption was determined across the pH range of 2.5 to 12. In addition, the Me2+ ions were contacted with freshly produced HFO and stored at a pH that dictated that 80 to 100% of the Me2+ would be in the sorbed state; desorbability of the Me2+ was determined as a function of Me2+‐oxide residence time. The change in the crystallinity of the HFO as a function of time was also monitored. The HFO aged without the Me2+ ions displayed no hysteresis between the adsorption‐desorption curves and no substantial shifts in fractional Me2+ adsorption were observed with pH throughout 21 wk of aging. The HFO aged with the Me2+ ions displayed increasing desorption hysteresis with time for Co2+ and Cd2+, but not Pb2+. The magnitude of hysteresis followed the order Co > Cd > Pb, which is the inverse of the ionic radii of the metal sorbates. While oxalate‐extractable Fe decreased with time during a 20‐wk period, powder x‐ray diffraction was unchanged during the same period. The data presented here suggest that Co and Cd are being incorporated into the metal oxide structure via recrystallization, but Pb remains associated with the surface and excluded from incorporation.

Lead coprecipitation with iron oxyhydroxide nano-particles

“…As shown below, one hypothesis to explain CPT from ADS is that CPT represents greater binding strength because of multiple surface sites. We tested this hypothesis by increasing the complexation constants for the weak site to the values proposed by Ainsworth et al (1994) and Dyer et al (2003). However, the SCM still did not fit the CPT data.…”

“…13). Some workers found the need for different, actually stronger, binding constants to fit their own adsorption experimental data (Ainsworth et al, 1994;Dyer et al, 2003). Dyer et al (2003) also developed a triple layer model, in which they used bidentate Pb 2+ complexes.…”

Efeito do pH na adsorção e dessorção de cádmio em Latossolos brasileiros

“…É amplamente relatado na literatura que os processos de adsorção de elementos-traço não são completamente reversíveis. Explicações para esse fato incluem: difusão dos elementos para o interior das partículas ou microporos dos óxidos (Backes et al, 1995;Gray et al, 1998); precipitação (Farrah & Pickering, 1978); incorporação na estrutura cristalina dos óxidos (Ainsworth et al, 1994) e readsorção ao adsorvente (Davis & Upadhyaya, 1996).…”

Sequential sorption of lead and cadmium in three tropical soils

“…In most cases, studies consid ering the sorption/desorption of Cd and Pb have indicated Pb was much less desorbable than Cd (Pardo, 2000;Adhikari and Singh, 2003). However, Ainsworth et al (1994) found Cd desorption to be less than that of Pb at pH 3 on aged hydrous iron oxide. It was suggested this was most likely due to the incorporation of Cd but not Pb into the oxide mineral structure.…”