Thermodynamic Properties for Arsenic Minerals and Aqueous Species

Arsenate and phosphate adsorption on ferrihydrite nanoparticles. Synergetic interaction with calcium ions

“…The optimized complexation parameters obtained for calcium in modelling scenario II, which excluded the formation of outer-sphere complexes, led to successful predictions of both the arsenate and calcium adsorption in the multicomponent systems. In order to consider in the modelling calculations the possible formation of insoluble arsenic-calcium mineral phases, solubility products, recently compiled by Nordstrom et al (2014), for different mineral phases (haidingerite, CaHAsO 4 ·H 2 O, log K sp = -4.79; tricalcium-arsenate, Ca 3 (AsO 4 ) 2 ·3H 2 O, log K sp = -21.14; johnbaumite, Ca 5 (AsO 4 ) 3 OH, log K sp = -40.12) were included in these simulations. Saturation indices were calculated for these mineral phases, and the results indicated that under the conditions analysed the multi-component systems were undersaturated and therefore no precipitation was expected.…”

Interactions of arsenic with calcite surfaces revealed by in situ nanoscale imaging

“…Given that arsenic may be either incorporated in the calcite crystal lattice or adsorbed at the mineral surface (Cheng et al, 1999;Román-Ross et al, 2006;Alexandratos et al, 2007;Sø et al, 2008;Yokoyama et al, 2009Yokoyama et al, , 2012, as in the case of ironoxyhydroxides, calcite may provide a long-term effective trap, since its dissolution usually takes place faster only under acidic conditions, but it is rather insensitive to superficial exchange and redox reactions. Moreover calcite dissolution in the presence of arsenic may induce the precipitation of a wide variety of calcium-arsenic phases (Pierrot, 1964;Ondrus et al, 1997;Nordstrom et al, 2014). All these features make calcite a suitable and probably underestimated mineral trap for arsenic.…”

“…Equilibrium constants used in PHREQC calculations, compiled fromMartínez-Villegas et al (2013) andNordstrom et al (2014).…”

Speciation dynamics of oxyanion contaminants (As, Sb, Cr) in argillaceous suspensions during oxic-anoxic cycles

“…The observed experimental sequence of Sb reduction followed by As reduction, suggests Sb reduction to Sb 2 O 3(s) , rather than to Sb(OH) 3 . Calculations are based on the thermodynamic values given in Bard et al (1985); Filella and May (2003); Nordstrom et al (2014); Tratnyek and Macalady (2000); Zotov et al (2003 detoxification is independent of the DOC concentration and not inhibited by O 2 (Table 2, R 10 ). Modelling results indicate that the persistence of As(III) in solution is consistent with its low sorption affinity to clay minerals (Table 3; Lin and Puls, 2000) and the under-saturation of the solution with respect to CaHAsO 3 (SI = −0.38).…”