Influence of HPO₄ ^2-, H₄SiO₄, Ca²⁺, Mg²⁺ on Fe floc growth and As(III) removal in aerated, natural groundwater

Influence of HPO₄ ^2-, H₄SiO₄, Ca²⁺, Mg²⁺ on Fe floc growth and As(III) removal in aerated, natural groundwater

de Ridder, D.J. (TU Delft Sanitary Engineering)
van de Wetering, T. S.C.M. (Brabant Water N.V.)
van Dijk, T. (Brabant Water N.V.)
van Halem, D. (TU Delft Sanitary Engineering)

2018-10-01

Our aim was to systematically investigate the influence of anions (HPO₄ ²⁻), cations (Ca²⁺, Mg²⁺) and neutral H₄SiO₄ on Fe flocculation and As(III) removal in the complex natural water matrix. For this purpose, three different anaerobic groundwaters were selected and manipulated by dosing of Ca²⁺, Mg²⁺, HPO₄ ²⁻, or by their removal by cation – and anion exchange. The change in Fe floc volume and of dissolved Fe and As were followed in aerated jar experiments. Fe floc growth was improved by addition of Ca²⁺ or Mg²⁺, and hindered by their removal. This hindered floc growth was more severe for groundwaters with higher P:Fe ratios, where Fe flocs carry a larger net negative surface charge, and rely stronger on Ca²⁺ or Mg²⁺ for charge neutralisation. When expressing the charge balance of the different groundwaters as the molar ratio (Ca²⁺ + Mg²⁺)/P, a linear relationship was found with the cumulative Fe floc volume, with a plateau at molar ratios >500. At environmentally relevant concentrations, H₄SiO₄ was found more likely to compete with As(III) for adsorption capacity than HPO₄ ²⁻. As(III) removal was strongly related to Fe removal - independent of Ca²⁺ or Mg²⁺ presence - indicating that As(III) is primarily adsorbed at an early stage in the flocculation process.

Arsenite adsorption
Iron floc growth
Natural groundwater

http://resolver.tudelft.nl/uuid:f487a55e-0bde-4de6-accc-0240c1feb6ba

https://doi.org/10.1016/j.jwpe.2018.07.004

2214-7144

Journal of Water Process Engineering, 25, 149-156

Institutional Repository

journal article

© 2018 D.J. de Ridder, T. S.C.M. van de Wetering, T. van Dijk, D. van Halem