| With the increasingly stringent environmental regulations,the flue gas denitrification technology represented by selective catalytic reduction?SCR?has been widely used,resulting in a large number of waste SCR catalysts.Although waste SCR catalysts are hazardous wastes,they contain considerable metals such as titanium,tungsten and vanadium,which have high economic value,and their resource utilization is of great significance.Aiming at the problem that the mineral phase is difficult to be separated and the elements are not easy to be separated during the treatment of waste SCR catalyst,this paper draws on the idea of Bayer method to treat bauxite,and puts forward and studies the treatment technology of waste SCR catalyst of"NaOH high pressure hydrothermal leaching-selective precipitation-acid decomposition".The process can effectively decompose vanadium-titanium waste catalyst,realize the separation of tungsten vanadium and titanium,especially the technology of selectively precipitating tungsten vanadium and hydrochloric acid to decompose tungsten vanadium slag,and solve the problem of extracting and separating tungsten vanadium in high alkaline solution.On the basis of fully extracting tungsten alum,the process maximizes the utilization rate of sodium hydroxide,greatly reduces the consumption of medicament,and improves economic and technical indicators.The main research contents and results of thisdissertation are as follows:?1?In the process of NaOH high pressure water hot leaching of waste SCR catalyst,the leaching rate of tungsten increased firstly and then decreased with the increase of temperature,but the vanadium leaching rate decreased with the increase of temperature and the overall low.on the other hand,the content of sodium in titanium slag increases significantly with increasing temperature,especially after the leaching temperature exceeds 180°C,and the sodium content of the slag rises more obviously.The XRD pattern of the leaching residue shows that when the leaching temperature is higher than 180°C,in addition to the anatase-type titanium dioxide,the characteristic peak of sodium titanate appears in the obtained leaching slag,which is the main reason for the increase of sodium in the leaching slag.The optimum conditions obtained by the experiment are temperature 180°C,liquid-solid ratio 3,alkali metal mass ratio 3:5.At this time,the tungsten leaching rate can reach 90%,and almost all of the titanium enters the slag.?2?The results of sodium leaching experiment showed that the method of boiled water could not effectively recover the sodium hydroxide in the slag.After 5 washings,the sodium content of the slag was only reduced by 41%,and the sodium content was still as high as3.8%.The hydrochloric acid washing process can effectively remove the sodium in the leaching slag.When the pH value of the washing end is 2,the sodium content of the leaching slag can be reduced to about 0.6%,thus,obtaining a high-purity high-titanium slag by-product.?3?The selective precipitation process of high alkali tungsten sputum shows that the high separation of tungsten and vanadium can be achieved by using agent C as a precipitant.When the optimum precipitation temperature is 95°C,the precipitation time is 2 h,and the dosage of the chemical C is twice the theoretical amount,the separation coefficient of tungsten and ruthenium is the largest.?4?The acid decomposition results of the precipitated slag showed that the decomposition rates of tungsten and vanadium initially increased with increasing temperature and reached the highest values at 70°C and 85°C,respectively.The concentration and amount of hydrochloric acid have little effect on the leaching of vanadium,but the effect on the leaching of tungsten is significant.When the acidity is high,tungsten forms a tungstic acid precipitate,and when the acidity is low,tungsten is dissolved in the solution as a heteropoly acid.The optimum conditions for acid decomposition are:reaction temperature 85°C,reaction time 2 h,HCl concentration 8 mol·L-1,and liquid-solid ratio 10:1.Under these conditions,the leaching rates of tungsten and vanadium respectively are 90%and 67%.?5?The adsorption behavior of D1008 resin on vanadium in hydrochloric acid solution accords with the Freundlich adsorption model.Under the condition that the high diameter ratio is 0.89 and the flow rate is 1 cm·min-1,D1008 resin is used to treat vanadium concentration 0.16g·L-1 acid,The dynamic adsorption experiment showed that the penetration capacity of wet resin to vanadium was 2.176 mg·mL-1,the dynamic exchange capacity after adsorption reached equilibrium was 4.416 mg·mL-1.When the flow rate was 1 cm·min-1 and the desorbent was 1 mol·L-1 NaOH solution,the vanadium concentration is the highest when the outflow liquid is 1.8 times times the volume of the resin,which is 2.57 g·L-1. |
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