Speciation of Zn in Blast Furnace Sludge from Former Sedimentation Ponds Using Synchrotron X-ray Diffraction, Fluorescence, and Absorption Spectroscopy

Blast furnace sludge (BFS), an industrial waste generated in pig iron production, typically contains high contents of iron and various trace metals of environmental concern, including Zn, Pb, and Cd. The chemical speciation of these metals in BPS is largely unknown. Here, we used a combination of synchrotron X-ray diffraction, micro-X-ray fluorescence, and X-ray absorption spectroscopy at the Zn K-edge for solid-phase Zn speciation in 12 BPS samples collected on a former BFS sedimentation pond site. Additionally, one fresh BPS was analyzed for comparison. We identified five major types of Zn species in the BFS, which occurred in variable amounts: (1) Zn in the octahedral sheets of phyllosilicates, (2) Zn sulfide minerals (ZnS, sphalerite, or wurtzite), (3) Zn in a KZn-ferrocyanide phase (K2Zn3[Fe-(CN)(6)](2)center dot 9H(2)O), (4) hydrozincite (Zn-5(OH)(6)(CO3)(2)), and (5) tetrahedrally coordinated adsorbed Zn. The minerals franklinite (ZnFe2O4) and smithsonite (ZnCO3) were not detected, and zincite (ZnO) was detected only in traces. The contents of ZnS were positively correlated with the total S contents of the BPS. Similarly, the abundance of the KZn-ferrocyanide phase was closely correlated with the total CN contents, with the stoichiometry suggesting this as cyanide phase. This study provides the first quantitative Zn speciation in BFS deposits, which is of great relevance environmental risk assessment, the development of new methods for recovering Zn and Fe from BPS, and potential applications of BFS as sorbent materials in wastewater treatment.