New application of a traditional analytical method - arsenic removal from water works sludge during iron(III) chloride coagulant production

The Marsh Test, the original means of determination of arsenic by hydride g eneration, has been modified to remove arsenic from water works sludge, wit h iron used instead of zinc as the main agent. Water works sludge (main com pound iron(III) oxyhydrate) generated during groundwater treatment can be e nriched in arsenic up to several g kg(-1). Acidic dissolution of this sludg e to produce FeCl3 coagulant liberates the arsenic. Addition of elemental i ron reduces this dissolved As(V) mainly to dispersed elemental As(O) partic les, which can be removed by filtration. If the reaction temperature is kep t below 50 degreesC, more than 99% of the arsenic can be removed from the c oagulant solution and less than 10% will escape as gaseous arsine (AsH3). S evere foaming and silicic acid gel formation occurs during the acidic disso lution, however. For technical and economic reasons the use of the water wo rks sludge for FeCl3 coagulant production is not competitive when compared with other recycling methods.