Titanium dioxide is an important chemical raw material and occupies an important position in the national economy. The production of titanium dioxide by the chlorination method mainly includes molten salt chlorination and boiling chlorination. Each ton of titanium dioxide needs to produce 0.5t ~ 0.6t Waste hydrochloric acid (HCl: 20% ～30%, Ti: 20 g/ L ～ 30 g/ L). Waste hydrochloric acid containing titanium impurities has no use value. Usually, the waste hydrochloric acid is directly discharged after simple neutralization, which not only causes a waste of resources but also seriously pollutes the environment, which is not in line with the national energy conservation and emission reduction policies and the development of circular economy policies.
Titanium mainly exists in three forms of TiO2+, TiOCl+, and TiOCl2 in the waste hydrochloric acid medium. With the increase of the concentration of hydrochloric acid or chloride ion, its main existence form changes from TiO2+ to TiOCl2 change. At present, the industrial processing methods for the by-product hydrochloric acid of chlorination titanium dioxide include chemical precipitation, ion exchange, extraction, and so on. The disadvantages of the chemical precipitation method are: consumes a lot of raw materials, produces a large amount of sludge, wastes acid, and valuable elements are not comprehensively utilized. The disadvantages of ion-exchange treatment of vanadium precipitation wastewater are complex equipment, large investment, and the need to regenerate the resin after use, which is troublesome to treat. In the extraction method, there are many extractants for titanium: acidic phosphorus extractants (such as D2EHPA, EHEHPA, HBT-MPP, etc.), neutral phosphorus-based extractants (such as TOPO, Cyanex923 etc.) and medium-strength alkaline extractant (such as N1923). The acidic extractant has good selectivity to titanium, but the extraction speed is slower, generally 1h ~ 2h, not suitable for industrial application; neutral phosphorus-based extractant has poor selectivity to titanium, and the neutral phosphorus-based extractant is expensive, medium-strength alkaline extractant (such as N1923) has low extraction saturation, and extraction time is 20min ~ 30min, the extraction t
