Recovery of vanadium and tungsten from waste selective catalytic reduction catalysts by K 2 CO 3 roasting and water leac
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Recovery of vanadium and tungsten from waste selective catalytic reduction catalysts by K2CO3 roasting and water leaching followed by CaCl2 precipitation Xianghui Liu1 • Qiaowen Yang1
Received: 22 February 2020 / Revised: 22 July 2020 / Accepted: 19 October 2020 The Author(s) 2020
Abstract Waste selective catalytic reduction (SCR) catalysts are potential environmental hazards. In this study, the recovery of vanadium and tungsten from waste SCR catalysts by K2CO3 roasting and water leaching was investigated. The roasting and leaching conditions were optimized: the leaching efficiencies of vanadium and tungsten were 91.19% and 85.36%, respectively, when 18 equivalents of K2CO3 were added to perform the roasting at 900 C for 2 h, followed by leaching at 90 C for 1 h. Notably, in the described conditions, the leaching rate of silicon was only 28.55%. Titanates, including K2Ti6O13 and KTi8O17, were also produced. Si removal was achieved in 85% efficiency adjusting the pH to 9.5, and the Si impurity thus isolated was composed of amorphous Si. Tungsten and vanadium were precipitated using CaCl2. At pH 10 and following the addition of 0.10 mol of H2O2 and 16 equivalents of CaCl2, the precipitating efficiencies of tungsten and vanadium were 96.89% and 99.65%, respectively. The overall yield of tungsten and vanadium was 82.71% and 90.87%, respectively. Graphic abstract Keywords Recovery Waste SCR catalyst K2CO3 roasting Water leaching CaCl2 precipitation
& Qiaowen Yang [email protected] 1
School of Chemical and Environmental Engineering, China University of Mining and Technology, Beijing, Ding No. 11 Xueyuan Road, Haidian District, Beijing 100083, China
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X. Liu, Q. Yang
1 Introduction Nitrogen oxide (NOx) emissions can trigger environmentally hazardous phenomena like photochemical smog and haze (Du et al. 2011; Thomas 1997). Therefore, in recent years environmental laws on NOx emissions have become increasingly strict in China. Due to its high efficiency and selectivity, the selective catalytic reduction (SCR) of NOx by ammonia to produce water and molecular nitrogen is the most popular approach to cutting NOx emissions (Forzatti 2001). The key component of SCR systems is the catalyst, which plays a fundamental role in the conversion of NOx to N2. The V2O5–WO3/TiO2 catalyst in NH3-SCR is widespread used in coal-fired power plants, as a result of the high activity of this catalyst and its tolerance to SO2 (Baiker et al. 1992; Wang et al. 2019). However, the lifespan of V2O5–WO3/TiO2 catalyst is limited by the activity of toxic substances present in flue gas, such as SO2, K2O, CaO, As2O3, and HgO (Kong et al. 2015; Li et al. 2016a, b; Li et al. 2018; Nicosia et al. 2007; Qi et al. 2017; Xu et al. 2017; Zhang et al. 2014). After several regenerations, these catalysts have been observed to become unable to catalyze NOx SCR (Huo et al. 2015; Wu et al. 2016). Notably, waste catalysts contain leachable hazardous metals, a trait that contributes to environmental concerns associated with their storage and
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