W And Mo Recovery And Separation With Simultaneous Hydrogen Production In Stacked Bioelectrochemical Systems

Rare metals W and Mo have a good physical and chemical properties,which have been widely used in daily life and production,but W and Mo were common existed in industrial waste water,recycling and separating W and Mo were technical problems,traditional chemical and electrochemical method have a high cost,complex process and secondary pollution.In recent years,bioelectrochemical systems(BESs)was a new technology,which was clean and effective of sewage treatment.Recovery and separation of metals through BESs had a lot of reports,it could deal with organic wastewater at anode and metals could be recycled and separated at cathode,no secondary pollution.Changing the connection number of reactor and the connection mode,the cathode potential of BESs could be changed and many metals of different redox potential could be recycled and separated.So this experiment will explore the coupling system of BESs for W and Mo recycling and separation.(1)At first,this experiment explored nine different connection modes.Stacked bioelectrochemical systems(BESs)of single unit serially matched with three parallel connected units was superior to the other stacked modes and can efficiently deposit and separate W and Mo with simultaneous hydrogen production.The single unit exhibited 27.6 ± 1.2%(W)and 75.4 ± 2.1%(Mo)deposits with separation factor of 8.1 ± 0.2 and hydrogen production of 0.34 ± 0.01 m3/m3 d,compared to 12.3 ± 0.9%(W),52.6 ± 2.2%(Mo)and 7.9 ± 0.5(separation factor)in the adjacent three parallel units.It comes down to under this kind of connection mode,single BES has more negative cathode and larger current density,and 3 parallel BESs acted as the power and part of electricity supply single BES,thus caused the difference between the two parts.In the controls,15.3 ± 1.7%(W)and 60.1 ± 1.6%(Mo)(single unit only),and 12.9 ± 1.3%(W)and 56.1 ± 2.0%(Mo)(three parallel units only)were achieved.These values were also 4.0(W)and 1.2(Mo)times(single unit),and 3.7(W)and 1.1(Mo)times(three parallel units)as those in the absence of Mo(VI)or W(VI).(2)The time process of W and Mo deposition and separation under single unit serially matched with three parallel connected units showed that,in the process of 1 ~ 6 h,single BES and 3 parallel BESs to W and Mo deposit showed increasing trend,in 6th hour,single BES exhibited 34.6±1.0%(W)and 80.8±0.8%(Mo)deposits;compared to 25.3±1.1%(W),59.1±1.4%(Mo)in the adjacent three parallel units.Further improved time,W and Mo deposition rate showed decreasing trend.This was because pH improved led to W and Mo dissolved.The acidic waste water of lower Mo and more W was more suitable for recovery and separation in coupling system,W and Mo could be completely separated under W:Mo=1:0.01.The acidic waste water of pH=2 was more suitable for recovery and separation in coupling system,low pH led to stainless steel electrode surface excess hydrogen evolution,was not conducive to W and Mo deposit,high pH was not suitable for W and Mo redox reaction,was not conducive to W and Mo deposits.Different composite electrode materials showed that,SSS-SSS was more effective for W and Mo recovery and separation,CR-SSS was more effective for hydrogen production,hydrogen production of 0.82±0.12 m3/m3 d was obtained.The Mo was completed removed and W and Mo were completed separated under the concentration of W and Mo were 0.05 mmol/L.This study demonstrates the feasibility of the stacked BESs for W and Mo deposition and separation,and the species of W(VI)and Mo(VI),and location of units were critical for efficient system performance.