Solar Oxidation and Removal of Arsenic at Circumneutral pH in Iron Containing Waters

Abstract

An estimated 30-50 million people in Bangladesh consume groundwater with arsenic contents far above accepted limits. A better understanding of arsenic redox kinetics and simple water treatment procedures are urgently needed. We have studied thermal and photochemical As(III) oxidation in the laboratory, on a time scale of hours, in water containing 500 micrograms/L As(III), 0.06-5 mg/L Fe(II,III), and 4-6 mM bicarbonate at pH 6.5-8.0. As(V) was measured colorimetrically, and As(III) and As(tot) were measured by As(III)/As(tot)-specific hydride-generation AAS. Dissolved oxygen and micromolar hydrogen peroxide did not oxidize As(III) on a time scale of hours. As(III) was partly oxidized in the dark by addition of Fe(II) to aerated water, presumably by reactive intermediates formed in the reduction of oxygen by Fe(II). In solutions containing 0.06-5 mg/L Fe(II,III), over 90% of As(III) could be oxidized photochemically within 2-3 h by illumination with 90 W/m2 UV-A light. Citrate, by forming Fe(III) citrate complexes that are photolyzed with high quantum yields, strongly accelerated As(III) oxidation. The photoproduct of citrate (3-oxoglutaric acid) induced rapid flocculation and precipitation of Fe(III). In laboratory tests, 80-90% of total arsenic was removed after addition of 50 microM citrate or 100-200 microL (4-8 drops) of lemon juice/L, illumination for 2-3 h, and precipitation. The same procedure was able to remove 45-78% of total arsenic in first field trials in Bangladesh.

Arsenic contamination of natural waters in San Juan and La Pampa, Argentina

“…Since the reporting of data from previous studies in Argentina, it has come to light that As III species in water are unstable in the presence of high concentrations of Fe III , causing oxidation of As III to As V (Gault et al 2005a;Gong et al 2002;Le et al 2000). This process can also occur from the photolytic reduction of nitrate to nitrite, which has been shown to convert up to 50 % of the As III to As V within 3 hours of collection (Hug et al 2001;Sharpless and Linden 2001). The use of opaque polyethylene bottles for water collection is one method to eliminate the effect of photochemical oxidation by omitting light exposure (Garbarino et al 2002).…”

Preparation and evaluation of a novel Fe–Mn binary oxide adsorbent for effective arsenite removal

“…To achieve higher arsenic removal, a pretreatment for As(III) oxidation is therefore usually involved, followed by coprecipitation/adsorption of the As(V) formed onto metal oxyhydroxides. Many oxidants or oxidant-generating systems have been tested for the oxidation of As(III) for example, O 2 and/or ozone (Kim and Nriagu, 2000), chlorine (Frank and Clifford, 1986), hydrogen peroxide (Pettine et al, 1999), manganese oxides (Driehaus et al, 1994;Oscarson et al, 1981;Stumm and Morgan, 1981;Scott and Morgan, 1995;Nesbitt et al, 1998), UV/iron systems (Hug et al, 2001), and TiO 2 =UV systems (Bissen et al, 2001). Due to their high oxidation potentials, ozone and hydrogen peroxide are not feasible for a specific oxidation of As(III), but result in side reactions with natural organic matter.…”

Fotocatálise heterogênea com TiO2 para oxidação de arsênio e sua remoção de águas por coprecipitação com sulfato férrico

“…4 Estes processos de remoção de arsênio geralmente envolvem um pré-tratamento de oxidação do As(III), seguido pela adsorção ou coprecipitação do As(V) formado usando adsorventes ou coagulantes. 4,11,12 No tratamento de águas, o As(V) pode ser removido pela coagulação e posterior coprecipitação com sulfato férrico e subsequente filtração do precipitado de hidróxido. O As(V) fica adsorvido sobre a superfície do hidróxido de ferro, podendo ser removido quase que quantitativamente.…”

“…4,[11][12][13][14] A oxidação pode ser realizada por oxidantes tais como oxigênio, ozônio, reagente Fenton, peróxido de hidrogênio, cloro, permanganato ou dióxido de manganês sólido etc. 12,15 Entre os processos de descontaminação ambiental que estão sendo desenvolvidos, os chamados "Processos Oxidativos Avança-dos" (POA) vêm atraindo grande interesse pela formação de radicais hidroxila (  OH), agente altamente oxidante.…”