Zirconium fumarate metal-organic framework: a selective adsorbent for fluoride from industrial wastewater

Many industrial processes produce high fluoride (150-450 mg/L) containing effluent. It may be recovered from the processing plants at the source. One effective technology is selective fluoride adsorption from the waste stream. Metal-organic frameworks (MOFs) are crystalline compounds with high surface area, pore volume, and tuneable pore channels and are suitable adsorbents. This study used zirconium fumarate (ZrFu) MOF to recover the fluoride from iron and steel industrial wastewater collected from blast furnaces and coke plants, respectively. In batch experiments, complete fluoride uptake from synthetic water (150 mg F/L) was obtained with 3 g ZrFu/L (q(e) = 49.66 mg/g), while for blast furnace (170 mg F/L) and coke plant (130 mg F/L) wastewater, 10 g ZrFu/L was required, (q(e) = 17 mg/g) and (q(e) = 13 mg/g), respectively. This difference in adsorbent dose was caused by interfering ions in industrial wastewater, which compete for the same adsorption sites as fluoride ions. Chemisorption was the rate-limiting step, and it conforms to the Langmuir isotherm and the pseudo-second-order model. Fluoride desorption was achieved in deionized water in 1 h. This suggests that the adsorption-desorption process could be scaled up to an industrial process to recover and re-use fluoride from wastewater.