Introduction
Toxic metal(loid)s found in industrial wastewaters often require expensive treatment. Passive filter bed systems are a cheaper alternative. We tested the potential of the ferric oxyhydroxysulphate mineral schwertmannite (Fe8O8(OH)x(SO4)y; x = 8 - 2y, 1 < y < 1.75) as an adsorbent to eliminate molybdenum (Mo), antimony (Sb) and tungsten (W) from industrial wastewaters. Schwertmannite adsorbents can be sustainably produced from a waste product of mining.
Material and Methods
In different wastewaters, the adsorption kinetics of Mo, Sb and W species onto the schwertmannite adsorbent SHM-sorpP were determined. For that purpose, 1 g/L SHM-sorpP was added to Sb contaminated wastewater (pH 4) and 20 g/L SHM-sorpP to Mo and W polluted wastewater (acidified to pH 3). Both were shaken for at least 15 days, sampled after different time intervals, filtered (0.20 µm) and analysed by ICP-OES.
Results
About 35 % of the initial Sb concentration (90 µmol Sb/g SHM-sorpP) were removed from the wastewater after 24 h. In a reference system with pH 7 (95 mM NaNO3, 5 mM NaHCO3, 1 g/L SHM-sorpP) the Sb elimination was more efficient with 50 % of initial Sb being adsorbed in 24 h (140 µmol Sb/g SHM-sorpP). This result could be related to the high phosphate concentration in the wastewater (> 1700 µmol/L), as phosphate is known to have a strong affinity towards schwertmannite and blocks binding sites. For Mo and W, 95 % (5 µmol Mo/g SHM-sorpP) and 93 % (80 µmol W/g SHM-sorpP) of the initial Mo and W concentration, respectively, were eliminated in 24 h.
Conclusions
Even though the obtained results will be tested in more practice-oriented filter bed experiments, they show that the schwertmannite adsorbent SHM-sorpP easily removes Mo and W from wastewater. In case of Sb the planned filter bed experiments will reveal the applicability of the schwertmannite adsorbents to treat such wastewaters.