Removal of Arsenic from Wet Scrubbing Wastewater

Abstract

Arsenic removal is hindered by its valence state. Addition of lime into wastewater containing arsenic gives benefits through the formation of low-soluble calcium arsenate, but the mechanism involved in the reduction of arsenic dissolution is not well known yet. Hence, in the present work different Ca/As ratios from 0 to 70% w/w were tested with the aim of finding the best conditions for removal of As from water (neutral tests) or solution (acid tests) containing sulphate ions. These solutions simulated aqueous streams coming from a wet scrubber for treatment of flue gas. Moreover, 5 g L^-1 of iron chloride were tested as additive in the acid tests.

In the optimum operating conditions, nearly 99% precipitation yield was obtained for both As(III) and As(V) in less than 1 h; the optimum process conditions were 10 g L^-1 of CaO without FeCl₃ for As(III) and 9 g L^-1 of CaO and 5 g ^-1 FeCl₃ for As(V) in acid solutions. As regards neutral solutions, 1 g L^-1 of CaO is enough to precipitate around 99% of As(III) whereas the same result for As(V) is achieved by a higher CaO concentration (40 g L^-1). Iron chloride had a negative effect on As(III) precipitation.