Synthetic wastewater was made up using deionized water with analytical grade KNO3 and KH2PO4. In order to simulate ionic strength of real wastewater the concentration of KNO3 was 0.01 mol/L [12]. 2 g pyrrhotite particles with the size of 0.3–0.6 mm and 50 ml wastewater were added in plastic tubes which were then flushed with N2 for 1 min before sealed. The tubes were placed on a rotator with a rotation speed of 20 rpm. This speed was selected, as it was fast enough to ensure complete mixing but not too fast so as to avoid centrifugation of particles.
In most of the adsorption experiment, the synthetic wastewater had the PO43−-P concentration and pH of 17.1 mg/L and 5.81, respectively, and the experimental temperature was maintained at 21 ± 0.5 °C. When studying the effects of pH of wastewater on P removal, the pH of wastewater was adjusted to specified pH values, in the range of 2.48 to 13.20, with 1 M KOH or 0.5 M H2SO4. P removal at was studied at three temperatures, 11.3, 21 and 29 °C. All batch adsorption experiments were carried out in triplicate, and the average data were presented.