Magnetic ball-milled FeS@biochar as persulfate activator for degradation of tetracycline.

• Ball-milled magnetic FeS@BC was synthesized successfully and it was applied in persulfate activation for the first time. • TC could be degraded in FeS@BC/PS system effectively after 30 min. • Surface-bond Fe(Ⅱ) and S(Ⅱ) participated in generation of SO 4 − and OH radicals. • BC acted as linker-transfer media to accelerate the degradation process in FeS@BC system. • Both of radical and non-radical degradation processes were involved in the FeS@BC/PS/TC system. In this study, composite of iron sulfide and biochar (FeS@BC) was synthesized successfully via physical ball milling and applied to the oxidative removal of tetracycline (TC) in the presence of persulfate (PS). Characterization results showed that FeS@BC, which has a small particle size, can be synthesized at a preset FeS-BC mass ratio. In addition, the ball-milled FeS@BC showed sufficient ferromagnetism. The effects of pH, dosages of FeS@BC and PS, and co-existing anions on TC degradation were investigated. Our results showed that TC degradation efficiency was enhanced at low pH and high dosages of PS and FeS@BC. Under optimal conditions (pH = 3.6, [FeS@BC] = 0.3 g/L and [PS] = 10 mM), a TC removal efficiency of 87.4% could be achieved after 30 min. Nevertheless, the TC removal rate was slightly inhibited by inorganic anions in the order of CO 3 2− > Cl− > NO 3 −. Surface-bound Fe(Ⅱ) and S(Ⅱ) acted as electron donors in the activation process and generated SO 4 − and OH at the surface of FeS@BC. In addition, S(Ⅱ) also participated in Fe(III) reduction. BC not only reduced the agglomeration of FeS, serving as a continuous source of effective Fe, but also acted as an electron shuttle and a suitable carbon-based adsorption material, facilitating fast electron transfer among PS, electron donors, and pollutants. Moreover, non-radical degradation processes might also exist in the FeS@BC/PS/TC system. The FeS@BC could be a promising effective activator for the remediation of other emerging organic contaminants. [ABSTRACT FROM AUTHOR]