Deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production in stacked bioelectrochemical systems (BESs): Impact of heavy metals W(VI)/Mo(VI) molar ratio, initial pH and electrode material

Abstract

The deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production was investigated in stacked bioelectrochemical systems (BESs) composed of microbial electrolysis cell (1#) serially connected with parallel connected microbial fuel cell (2#). The impact of W/Mo molar ratio (in the range 0.01 mM : 1 mM and vice-versa), initial pH (1.5 to 4.0) and cathode material (stainless steel mesh (SSM), carbon rod (CR) and titanium sheet (TS)) on the BES performance was systematically investigated. The concentration of Mo(VI) was more influential than W(VI) in determining the rate of deposition of both metals and the rate of hydrogen production. Complete metal recovery was achieved at equimolar W/Mo ratio of 0.05 mM : 0.05 mM. The rates of metal deposition and hydrogen production increased at acidic pH, with the fastest rates at pH 1.5. The morphology of the metal deposits and the valence of the Mo were correlated with W/Mo ratio and pH. CR cathodes (2#) coupled with SSM cathodes (1#) achieved a significant rate of hydrogen production (0.82 ± 0.04 m/m/d) with W and Mo deposition (0.049 ± 0.003 mmol/L/h and 0.140 ± 0.004 mmol/L/h (1#); 0.025 ± 0.001 mmol/L/h and 0.090 ± 0.006 mmol/L/h (2#)).

Sequential anaerobic and electro-Fenton processes mediated by W and Mo oxides for degradation/mineralization of azo dye methyl orange in photo assisted microbial fuel cells

“…The metals leaching at a high pH was caused by the significant increase in the effluent pH ( Fig. 6D), because the solubilities of W and Mo deposits increases exponentially at higher pH values [14,27,31]. SEM, EDS and XRD further validated these observations.…”

“…The W and Mo oxides deposited on graphite felt electrodes were prepared in-situ. Briefly Co., Ltd., analytically pure) with each metal concentration of 200 mg/L [30,31]. The pH of catholyte was set to 1.5 and the MFCs were operated for 6 h with air sparging at a rate of 80 mL/min [27].…”

Preferable Individual Rather Than Sequential Feedings Under Air Exposure Conditions for Deposition of W and Mo in Stacked Bioelectrochemical Systems

“…In parallel, the reductive cathode electrodes of BESs can deposit many heavy metals from aqueous solutions, providing an environmentally benign approach for heavy metal recovery in the cathode with simultaneous organic degradation in the anode (Wang and Ren, 2014;Dominguez-Benetton et al, 2018). The stacking of BESs, composed of multiple MFC and/or MEC units, can efficiently deposit and separate many mixed metals on the cathode, including Cu(II), Co(II), and Li(I), and W(VI) and Mo(VI) based on their different redox potentials as well as the various circuital currents and cathode potentials created by the purposely diverse connections of multiple MFC and/or MEC units in serial and/or parallel connections (Huang et al, 2014(Huang et al, , 2017(Huang et al, , 2018Wu et al, 2015;Zhang et al, 2015). The stacked BESs are regarded to be promising for hydrogen production because of their higher performance than increasing the size of an individual unit through reduced mass transfer losses during upscaling (Sun et al, 2008).…”

“…In parallel, the sequential feeding, termed as the effluents of the first units of the stacked BESs fed into the subsequent units in serial connection (Lanas et al, 2014), might be suitable for recovery of more heavy metals from the final effluents owing to the successive organics oxidative reactions in the same feeding influent at a long hydraulic retention time (HRT) (Lanas et al, 2014). Compared with the attention on electrically stacked BESs in serial or parallel connections for metal recovery (Huang et al, 2014(Huang et al, , 2017(Huang et al, , 2018Li et al, 2019), the impact of such different modes of flow feeding on the metallurgical stacked BESs has been scarcely reported.…”

“…In this study, we evaluate continuous-operated stacked BESs with individual or sequential flow modes in the presence or the absence of dissolved oxygen to assess deposition and separation of mixed W(VI) and Mo(VI). These two species are always concomitantly present in the ore dressing wastewater and the leaching liquors of many spent catalysts in key industries, such as the automotive industry (Lasheen et al, 2015;Huang et al, 2017Huang et al, , 2018Huang et al, , 2019. Individual rather than sequential feedings under air exposure conditions achieved efficient W and Mo deposition and separation.…”