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

More attention has been paid to the deterioration of water bodies polluted by drinking water treatment sludge (DWTS) in recent years. In this study, a novel investigation for recovery of Al and Fe from DWTS has been conducted, which are used for the synthesis of a magnetic nanosorbent (ALCS-Fe-AL) by loading Al/Fe oxides onto acid leaching carbonized sludge (ALCS). And 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. Key factors, including the content of Fe and Al in the adsorbent, adsorbent dosage and initial pH of aqueous solution, were investigated. The results showed that ALCS-Fe-AL (ALCS:Fe=3:3 & ALCS-Fe:Al=3:6, mass ratio) can remove 97.17% F (initial concentration is 10 mg/L) at pH=7, T=25°C and adsorbent dosage of 3.0 g/L. The absorbent could reduce the fluoride concentration to below 1.0 mg/L in drinking water which meets the level of drinking water standard recommended by the World Health Organization (WHO). In addition, it had a high selectivity for fluoride versus common 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, and the maximum adsorption capacity reached a high value of 30.49 mg/g. The adsorption kinetics followed a pseudo-second order model. These properties showed that the ALCS-Fe-AL is a promising adsorbent for fluoride removal from drinking water.