Recycling of iron and aluminum from drinking water treatment sludge for synthesis of a magnetic composite material (ALCS-Fe-Al) to remove fluoride from drinking water

In this study, a novel investigation for recovery of Al and Fe from drinking water treatment sludge (DWTS) has been conducted, which are used for the synthesis of a magnetic composite material (ALCS-Fe-Al) by loading Al/Fe oxides onto acid-leached carbonized sludge (ALCS). The low-cost magnetic adsorbent which can be easily separated from water by a magnet was tested for the ability to remove fluoride from drinking water. The most effective adsorbent ALCS-Fe-Al was prepared under the following conditions: ALCS:Fe = 1:1 & (ALCS-Fe):Al = 1:2. While the preparation conditions of the adsorbent ALCS-Fe-Al* prepared according to the actual iron and aluminum contents in the sludge are: ALCS:Fe = 1:1 & ALCS-Fe:Al = 2:1. Both of the two adsorbents could reduce the fluoride concentration to below 1.5 mg/L in aqueous solution at pH = 7, T = 25 °C with a adsorbent ratio of 3g/L, which meets the level of drinking water standard recommended by the World Health Organization (WHO). In addition, it had a relatively high selectivity for fluoride versus common competitive co-existing ions and high fluoride removal efficiency in a wide range of initial pH of 4-9. At neutral initial pH, the adsorption isotherm was well fitted with the Langmuir model. The maximum adsorption capacity reached 30.49 mg/g. The adsorption kinetics followed the pseudo-second-order model. Furthermore, the adsorption performance, composition and adsorption mechanism of the adsorbent can be proved by SEM, BET, VSM, XRD and XPS. This work provides a new idea for full utilization of DWTS as adsorbent for fluoride removal from drinking water.