Optimization of Roasting Parameters for Recovery of Vanadium and Tungsten from Spent SCR Catalyst with Composite Roasting

Abstract

Every year, large amounts of selective catalytic reduction (SCR) catalysts with losing catalytic activity and failing to be regenerated need to be regenerated, which will result in acute pollution. Recycling valuable metals from spent SCR catalysts can not only solve environmental problems, but also save resources. The process of sodium roasting and water leaching is able to effectively extract vanadium (V) and tungsten (W) from spent SCR catalysts. To improve the efficiencies of V and W, different sodium additives were first investigated in the roasting process. The results revealed that the process of NaCl-NaOH composite roasting and water leaching showed superior leaching efficiencies of V and W, which can reach 91.39% and 98.26%, respectively, and simultaneously, it can be found that adding low melting point NaOH promoted mass transfer as compared with the melting points of different sodium additives. Next, a single-factor experiment was conducted to investigate different roasting conditions, such as roasting temperature, roasting time, mass ratio of sodium additive and catalyst, and mass ratio of NaCl and NaOH, on the leaching efficiencies of V and W. Then, a three-level and four-factor orthogonal experiment and a weight matrix analysis were used to optimize the roasting parameters. The results showed that roasting temperature had the most significant effect on the leaching efficiencies of V and W, and the optimal roasting conditions were as follows: the roasting temperature was 750 °C, the roasting time was 2.5 h, the mass ratio of sodium additive and catalyst was 2.5, and the mass ratio of NaCl and NaOH was 1.5. Under the optimal roasting conditions, the leaching efficiencies of V and W were 93.25% and 99.17%, respectively. The results of XRD analysis inferred that VO2 coming from the decomposition of VOSO4 in spent SCR catalysts may first oxidize into V2O5 and then react with sodium additives to produce NaVO3. The formation of titanium-vanadium oxide ((Ti0.5V0.5)2O3) was a part reason of hindering the leaching of vanadium. With the increase of roasting temperature, TiO2 converted into Na2Ti3O7, which indicated that the main structure of the catalyst was destroyed, and simultaneously, more characteristic peaks of sodium metavanadate and sodium tungstate appeared, thus enhancing the leaching of V and W. Finally, it can be seen that the process of NaCl-NaOH roasting and water leaching remained higher leaching efficiencies of V and W and lower roasting temperature by comparing with leaching efficiencies of V and W in different processes of recycling SCR catalyst. The process of NaCl-NaOH composite roasting and water leaching provided a strategy with a highly efficient and clean route to leach V and W from spent SCR catalyst. The orthogonal experiment and weight matrix analysis in our study can be used as a reference to optimize the reaction conditions of a multiple indexes experiment.

Comparative study for leaching processes of uranium, copper and cadmium from gibbsite ore material of Talet Seleim, Southwestern, Sinai, Egypt

“…These results show that roasting time has a direct impact on the leaching efficiency of uranium, copper and cadmium with leaching efficiency increasing from 80%, 75%, and 70 to 90%, 89%, and 83% at 3 h, respectively. At 4 h, the metal values' leaching efficiency decreases because roasted ore showed caking, which caused leaching of part elements to become more difficult [55]. Thus, 3 h considered as the best roasting time.…”

Strategy and Technical Progress of Recycling of Spent Vanadium–Titanium-Based Selective Catalytic Reduction Catalysts

“…The leaching residues of nano-TiO 2 and sodium titanate nanowires were also used as heavy metal adsorbents. The addition of NaCl allowed decomposition-generated chlorine Cl 2 to act as a catalyst and oxidant to promote the oxidation of low-valent V, thus facilitating the leaching of V. Wang et al 103 compared different types of sodium additives and found that the leaching efficiency of NaOH−NaCl roasting for V and W was up to 91.39% and 98.26% higher compared to acid and alkaline leaching, respectively. At the same time, the addition of low melting point NaOH promoted the reaction to a greater extent than the addition of sodium additives with different melting points.…”

Phase Equilibria and Phase Diagram of the Quaternary NaOH–Na3VO4–Na2WO4–H2O System at 278.15 K to 353.15 K

“…8 This system shows excellent catalytic properties, such as a wide operating temperature window and high denitration rate. 9 Spent SCR catalysts are increasingly generated from corresponding industrial sectors 10,11 and are gaining more attention given their very high concentration of strategic as well as base metals like vanadium, tungsten, and titanium. 12 The spent SCR catalyst is subjected to recycling through an integrated hydrometallurgical route 13,14 to recover the valuable metal and simultaneously address the resulting global environmental issues.…”