Separation and recovery of V/W/Na from waste SCR catalyst leaching solution using membrane electrolysis – Ion morphology pretreatment solvent extraction-stripping method

Abstract

In this study, a cleaner method for separation and recovery of V/W/Na in waste Selective catalytic reduction (SCR) catalyst alkaline leaching solution was proposed. The method involved membrane electrolysis followed by ion morphology pretreatment and solvent extraction. An acidic V(V)/W(VI) solution was obtained using the membrane electrolysis method without adding any other chemical reagents. In addition, Na was recovered in the form of NaOH by product, avoiding the generation of Na containing wastewater. The electrolysis parameters were investigated, the lowest power consumption of 3063 kW·h·t⁻¹ NaOH was obtained at a current density of 125 A·m⁻²and an initial NaOH concentration of 2 mol·L⁻¹. After electrolysis, oxalic acid was added to the acidic V/W containing solution, converting V(V) negative ion to V(IV) positive ion. Since W(VI) ion state remained in negative form, the generation of heteropolyacid ions (W_xV_yO_zⁿ⁻) was prevented. It was found that under the condition of oxalic acid addition/theoretical consumption 1.2 and reaction temperature 75 °C, 100% V(V) was converted to V(IV). Using 10% N263 + 10% n-octanol+80% sulfonated kerosene as extractant, the highest W(VI)/V(IV) separation coefficient of 7559.76 was obtained at pH = 1.8, O:A ratio = 1:1 and extraction time 15 min. With 2 mol·L⁻¹ NaOH as stripping reagent, the W stripping efficiency reached 98.50% at O:A ratio = 2:1 after 4-stages of stripping. The enrichment of V remained in the solution was realized using P204 as extractant and 20% (mass) H₂SO₄ as stripping reagent. The parameters of extraction/stripping process were investigated, using 10% P204 + 10% TBP+80% sulfonated kerosene as extractant, the V extraction efficiency reached 97.50% at O:A ratio = 1:2 after 4 stages of extraction. Using 20% H₂SO₄ as the stripping reagent, the V stripping efficiency was 98.30% at an O:A ratio of 4:1 after five stages of stripping. After the entire process, a high-purity VOSO₄ and Na₂WO₄ product solutions were obtained with V/W recovery efficiency 95.84%/98.50%, separately. This study examined a more effective and cleaner method for separating V/W/Na in Na₂WO₄/NaVO₃ solution, which may serve as a reference for the separation and recovery of V/W/Na in waste SCR catalysts.