Removal of fluoride and arsenic from waters with acidic pH

ULACCO S. B.; NARIO N; MEIER L. A.; FUENTE, S. A; VIDAL E.; GRÜNHUT M.; DOMINI C; MORGADE C. I. N.

Buenos Aires

Congreso; WCCE11 - 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Asociación Argentina de Ingenieron Químicos

The presentwork shows partial results of a larger study in development, of the adsorptiveand photocatalytic activity of different oxides for sodium fluoride and arsenicoxide in water. Although both elements are a problem in groundwater in variousareas of the planet, generally slightly alkaline, they are also a problem inwater of industrial origin. Therefore, the behavior at different pH of theoxides studied acquires special relevance. Theparticular objective of this part of the work is to obtain at low pH (pH=3) thepercentage of removal of fluoride and arsenic (III). In all cases, the oxidesare below the respective isoelectric points, so they are positively charged.The determinations were made at room temperature (20°C) with a concentration of1g/L of each oxide. The initial concentration was 5 ppm NaF (Merck, analyticalgrade) and 200 ppb for As2O3, being the World Health Organization recommendations1.5 ppm for fluoride and 10 ppb for arsenic. Rutile TiO2, anatase TiO2, MgO andFe2O3 were studied. The determination of the concentrations for fluoride anionwere carried out with a selective electrode Orion pH/ISE meter 710 (Van LondonCo) while the determination of As(III) was based on the inhibitory effect ofthis species on the discoloration of a helianthin solution caused by theproducts of the oxidation-reduction reaction between potassium bromate andhydrochloric acid. Helianthin decolorization was monitored on an Agilent 8453spectrophotometer at 508 nm [1]. All determinations were performed intriplicate. The results obtained show that rutile TiO2 and MgO are more effectivefor fluoride removal in the absence of light, 65.5% and 68.6% respectively.While, anatase TiO2 and Fe2O3 for the removal of As(III), 69% and 46%respectively. On the other hand, in the presence of light, rutile TiO2 has animportant photocatalytic effect both in the removal of F- and As(III), reachinga removal percentage of 58% and 75.8% respectively. Anatase TiO2 is effectiveto remove As(III) (73.7%). From theresults obtained it can be observed that at pH=3 the best removal is byadsorption, being MgO the best adsorbent followed by rutile TiO2. Thisconclusion is in agreement with the percentages of ionic character of themetal-F- bonds, which are respectively 86% for Mg-F, 79% for Ti-F and 70% forFe-F. The case of anatase TiO2 is known to present a particular behavior, sinceF- binds preferentially to O atoms inside the crystalline structure, whichdetermines a very low adsorptive activity for the anion [2]. As for arsenic,the best removal is produced by photocatalysis with polymorph rutile TiO2. Atthe pH studied, it is planned to study the competitive removal efficiency forboth contaminants with rutile TiO2, which compared to the isolated studiespresents the best comparative performance. References 1. Afkhami A., Madrakian T., Assl A.A., Talanta 55 (2001)55-60. 2. L.A. Meier, A.B. Schvval, S.B. Ulacco, A.S. Lorenzetti,E. Vidal, C. Domini, C.I.N. Morgade (2022). Study of phase-pure TiO2 for the removal of fluorides in water.Materials Today Communications 31(103389), 1-9.