The influential mechanisms of solution chemistry on the stability and transport of vanadium-titanium magnetite tailing colloids

Vanadium-titanium magnetite tailing colloids (TCs) from mineral weathering and industrial production can cause overlooked vanadium groundwater pollution due to their mobility and releasable vanadium. This study investigated the stability and transport mechanisms of vanadium-titanium magnetite TCs under various solution chemistries, including pH, ionic strength (IS), acetic acid (AA), oxalic acid (OA), and citric acid (CA), via field survey, batch, and column experiments with numerical modeling. The results showed field-existing evidence of TCs, AA, OA, and CA in the groundwater of the V-Ti magnetite tailing pond. The edge-face interaction between TCs promoted TCs aggregation around the isoelectric point. AA promoted, while OA and CA inhibited TCs aggregation under all pH and IS. Stronger aggregation was induced by the increased concentration of AA, but contrary to OA and CA. The critical coagulation concentration (CCC) of TCs changed from 34.83 mM to 2.04, 424.54, and 561.17 mM after adding 10 mM AA, OA, and CA at pH 7. As the concentration of LMWOAs increased, stronger aggregation was induced. Increasing solution pH and decreasing IS promoted TCs transport. The ripening phenomenon occurred in the BTCs when IS exceeded 30 mM. AA inhibited TCs transport under acidic and neutral conditions by forming AA-TC-quartz sand ternary complexes, while OA and CA promoted transport at all pH. The variation of acid concentration showed insignificant effects on the TCs transport. DLVO and XDLVO interactions highly regulate TCs stability and transport, and the Langmuirian blocking and ripening featured retention profiles of TCs can be well described using the modified reactive transport model, the Langmuirian kinetic equation and the ripening kinetic model. This research is the first systematic study of vanadium-titanium magnetite TCs behaviors under different solution chemical conditions, and provided a novel strategy for groundwater pollution prevention of TCs by considering plants capable of secreting AA.