| Titanium dioxide(TiO2)pigments are widely used in paints,paper,food,pharmaceuticals,cosmetics and etc.The production methods of TiO2 are constantly being improved as the consumption of TiO2 in the world is increasing every year.Currently,the hydrochloric acid(HCl)process has become popular technology in the production of TiO2,due to its advantages of wide sources of raw materials,less waste and high economic value.However,the current HCl process still has many defects,such as long extraction steps,the use of organic solvents and insufficient research on extraction mechanism.In order to improve the shortcomings of HCl process,in this paper,the ilmenite HCl leachate is applied as raw material.First,a shorter step simultaneous extraction system of ferrotitanium and a safer extraction system of hydrophobic deep eutectic solvents(HDESs)/magnetic ionic liquids(MILs)are established.Second,the Ti solution and Fe solution are hydrolyzed to prepare TiO2 and Fe2O3,respectively.Finally,the extraction mechanism of titanium and iron is revealed at the atomic level by combining density functional theory calculation and spectral analysis.A simultaneous extraction system C18H37NO/ROH is established for the simultaneous extraction of Ti and Fe from the HCl leachate of ilmenite,in order to solve the problem of long extraction process in HCl process.The extraction and separation of titanium and iron are realized by one-step extraction.The results show that C18H37NO/ROH has high selectivity for Ti and Fe and the simultaneous extraction of titanium and iron can be effectively separated.The purity of Ti solution and Fe solution obtained are 98.75%and 99.18%,respectively,after simultaneous extraction and stepwise stripping.Based on the current HCl process uses organic solvents,safer HDESs extraction system is designed in order to improve the safety and environmental friendliness of TiO2 produced by HCl process.The reaction behavior of Ti,Fe,Mg,Ca,Al,V,Mn and Cr in the ilmenite HCl leachate during extraction,scrubbing and stripping is comprehensively studied.The results display that the coextracted impurity metal ions are effectively removed and the purities of Ti solution and Fe solution obtained by stripping are 99.76%and 99.74%,respectively.Since the research metrics of HCl process only include extraction efficiency and solution purity,the extraction system of MILs and HDESs is used in combination and the physicochemical properties and toxicity of the reagent are studied.The results show that the cationic ligand RCNO removes 99.98%Fe.Meanwhile,the RCNO has low viscosity(14 mPa·s),less loss to the aqueous phase(424.303 mg/L),and no phase change physicochemical properties.The Fe solution with purity of 99.82%is recovered in the process of RCNO regeneration.The HDESs are used to directly and selectively extract Ti from ilmenite HCl leachate after removal of Fe.The results show that HDESs-4 has the physicochemical properties of low density(0.8602 g/cm3),low viscosity(10 mPa·s)and low water solubility(53.15 mg/L).The purity of Ti solution obtained is 99.87%through extraction,scrubbing and stripping.Compared with other methods,the toxicity of MILs and HDESs is lower by detecting the toxicity of reagents through cell activity test.In order to realize practical application of Ti solution and Fe solution,the extraction scale-up test is carried out first.The hydrolysis process is studied after the organic substances in the solutions are removed by activated carbon adsorption.The results show that the hydrolysis equilibrium of Ti solution is achieved in 2 hours when the hydrolysis temperature is 180 ℃.The crystal form of TiO2 is rutile,and the purity of TiO2 is 99.87%when the calcination temperature is 900℃.The Fe solution is hydrolyzed to form aFe2O3 nanoparticles and the crystal form of α-Fe2O3 is enhanced with the increase of hydrolysis time.The purity of α-Fe2O3 reaches 99.90%.The mechanism of extraction of Ti and Fe from HCl solution by C18H37NO/ROH is revealed by analyzing the speciation of Ti and Fe,slope method and FT-IR characterization.The results demonstrate that most of Ti in HCl solution is extracted byOH of ROH through ion association,and the structure of the extracted complex is[TiOCl3]2[(ROH)H2].The-OH of ROH extracts Fe through ion association and solvation,and the structures of the extracted complexes are[FeCl4][(ROH)3 33H]and[FeCl3][(ROH)3.33],respectively.The-C=O of C18H37NO extracts Fe through ion association,and the structure of the complex is[FeCl4]3[(C18H37NO)3H3].In order to clarify the mechanism of HDESs-4 extraction of Ti and Fe at the atomic level from HC1 solution.First,the effects of H2O,HBD,HBA,Cl-and H+on the extraction of Ti and Fe are studied by slope method.Then,density functional theory calculations,FT-IR spectra and 1H-NMR spectra are utilized.The results show that HDESs-4 removes H2O during the extraction of Ti and Fe.In HDESs-4,the lone pair electrons on O in-OH of HBD form coordination bonds with Ti of the neutral molecule TiOCl2,and the structure of the complex is(TiOCl2)2(HBD)(HBA)(HCl).HBA and HBD firstly form complex cation HBA-H+and HBD-H+,respectively,with H+in HCl solution.Then,the HBA-H+and HBD-H+extract FeC14-due to ion association and the structure of the complex is(HBA)4(FeCl4-)0.5(H+)0.5(HBD).The extraction reaction of impurity metal ions in HCl solution by HDESs-4 is studied by analyzing the extraction reaction of HDESs-4 in HCl solution,the speciation of impurity metal ions and FT-IR spectrum characterization.The results show that the mechanism of the extraction of Mg and Ca from HCl solution by HBAis cation exchange,and the structure of the extract complex is[M(HBA)2]2+.The mechanism of extraction of Al,V and Mn from HCl solution by HBA is ion association,and the structure of the complex is[HBA-H][MClX].The mechanism of extraction of Cr from HCl solution by HBA and HBD is ion association,and the structure of the complex is[HB A-H][MClx]2[HBD-H]. |
