Abstract

The optimal conditions to remove arsenic(III) from a solution were fitted using a factorial experimental design in a reaction catalysed by visible light (black light, 360 nm) and an iron-citrate complex. Experiments were performed by simultaneously modifying the two variables affecting the removal of arsenic, i.e. iron and citrate concentrations. The single polynomial function obtained with the factorial design methodology indicates that the iron concentration was the most critical parameter in the removal of arsenic by precipitation. Mathematically, it was determined that the optimum molar ratio for arsenic, citrate and iron was 1:4.5:18.7, respectively, over 90% of arsenic being eliminated after 4 h of irradiation. The comparison between the As(III) and As(V) co-precipitation rates indicates that almost 80% of As(III) was removed after 1 h of irradiation with black light, while As(V) required 4 h of irradiation to reach the same value. When natural water containing approximately 1 mg L-1 of arsenic, only as As(V), was irradiated with solar light under optimised conditions, approximately 95% of the arsenic was removed after 1 h of irradiation. © 2006 Society of Chemical Industry.