Calcium oxalate/calcium silicate hydrate (Ca-Ox/C-S-H) from blast furnace slag for the highly efficient removal of Pb2+ and Cd2+ from water

Heavy metal pollution of water is a global environmental concern which necessitates viable remediation through the exploration of highly effective adsorbents. Based on the affinity between oxalate and heavy metal, we synthesized a novel calcium oxalate/calcium silicate hydrate (Ca-Ox/C-S-H) adsorbent from blast furnace slag (BFS) by a facile oxalic acid/NaOH treatment. The BFS-derived Ca-Ox/C-S-H exhibited superior maximum uptake capacities for Pb2+ (2117 mg g-1) and Cd2+ (1083 mg g(-1)). The removal mechanism involves ion exchange, and adsorption kinetics showed an equilibration time of 10 min for Pb2+ at a solid-to-liquid ratio of 1.0 g L-1, in agreement with both the pseudo-first- and pseudo-second-order reaction kinetics models. The adsorption isotherms of Ca-Ox/C-S-H for both metal ions also fitted the Sips model well. Ca-Ox/C-S-H showed high selectivity toward Pb2+ among various heavy metals and coexisting ions in water, and demonstrated high retention of adsorption capacity after being recycled up to four times. These results support the use of BFS-derived Ca-Ox/CS-H as an efficient and economical Pb2+ and Cd2+ adsorbent.

Automated summary

The novel calcium oxalate/calcium silicate hydrate (Ca-Ox/C-S-H) adsorbent synthesized from blast furnace slag (BFS) exhibits superior maximum uptake capacities for Pb2+ (2117 mg g-1) and Cd2+ (1083 mg g-1). The adsorption mechanism involves ion exchange and equilibration time for Pb2+ is 10 minutes at a solid-to-liquid ratio of 1.0 g L-1, in accordance with both pseudo-first- and pseudo-second-order reaction kinetics models. The adsorption isotherms of Ca-Ox/C-S-H for both metal ions also fit the Sips model well. The adsorbent shows high selectivity towards Pb2+ among various heavy metals and retains high adsorption capacity even after being recycled multiple times.