•Rapid selective extraction of V(V) from leaching solution was reached using ACCs.•The 99.7 wt% of NH4VO3was obtained by the two-step separation method.•The sulfated primary amine N1923 was used for the extraction separation of V(V) and Cr(VI)•The second step of separation of stripping was investigated.The efficient and rapid selective extraction of V(V) from leaching solution with sulfated primary amine N1923 was demonstrated. In the single-stage extraction using annular centrifugal contactor (ACC), the influence of the total flow and the speed rotor on extraction percentage of V(V) was investigated using central composite design (CCD), and the results of experimental conditions were analyzed by analysis of variance. The current concentrations of V(V) and Cr(VI) in leaching solution were 23.70g/L and 1.52g/L, respectively. 99.6% of vanadium was extracted and separated from the aqueous solution by employing four-stage countercurrent extraction with annular centrifugal contactors (ACCs). The total contact/resident time of the two phases was 4.8 min, and the separation factor of V(V) and Cr(VI) was 273.9. The two metals in leaching solution can be separated primarily, and then 23.61g/L V(V) and 0.72g/L Cr(VI) in loaded organic phase can be further separated by the stripping. The NH4VO3 with purity of 99.7% was obtained by two steps of separations and studied by the analyses of XRD, SEM and particle size distribution (PSD). The reactions of extraction and stripping in the separation processes were investigated in order to establish a firm conclusion.Download high-res image (121KB)Download full-size image

•Configuration of BMED stack was improved to increase the recovery of citric acid.•An acid recovery rate of 97.1% was reached with 3.3% sodium citrate at 40 mA cm−1.•Pure base was obtained for reuse by filling mixed resins in base compartment.•Voltage across acid compartment was greatly reduced by filling cation resins in it.•BMED would be a promising technology to recover citric acid from fermented liquid.The process of recovering citric acid from fermented liquid by bipolar membrane electrodialysis (BMED) was studied. Two bipolar membranes and one cation exchange membrane were stacked to form a two-compartment BMED stack configuration. The effects of the current density, initial concentration of sodium citrate, and structure of the acid compartment (AC) and base compartment (BC) on the performance of the BMED process were investigated. Filling mixed-bed ion exchange resins in BC could decrease the compartment resistance and led to a pure base solution for reuse. The highest acid recovery of 97.1% was achieved with 3.3% initial sodium citrate under a current density of 40 mA cm−1. Additionally, a decrease of voltage across AC by filling cation exchange resins restricted the migration of H+ ions from AC to BC. A higher initial concentration of sodium citrate has an adverse effect on the recovery of citric acid. BC with a bipolar membrane (BPM) exhibited lower energy consumption and a higher recovery rate of citric acid. BMED appears to be a promising technology for recovering citric acid from fermented liquid.

•The ED process is optimized from two membrane configurations including one stage with one passage and with two passages.•Comparing with other studies treating the similar concentration feed water, the ED process is more energy-saving.For the high pressure and high energy consumption of Seawater reverse osmosis (SWRO) desalination technology, an energy-saving “NF/EDR” integrated membrane process for seawater desalination was proposed in our study. The seawater desalination by Nanofiltration (NF) membrane with high desalination capacity has been reported in our previous paper. This manuscript is the second part of this system about the optimization of electrodialysis (ED) process, where ED process with polarity reverse (EDR) was applied to treat the NF output with the conductivity of 8790 μS/cm. A series of operation parameters of the ED process were optimized. More specifically, the effects of the concentrate and dilute flow, internal water flow model, as well as temperature of raw water on separation performances were well investigated. Besides, the optimal period of polarity reverse was determined. The results showed that with the dilute stream flow of 150 L/h, concentrate stream flow of 120 L/h and the ED stack consisted of one stage with two passages, with the proportion of 27/23 in cell pairs, together with suitable raw water temperature, the desalination rate of ED process could be about 90% and the energy consumption was 0.98 KWh/(m3 produced water). Furthermore, the membrane fouling could be effectively avoided by EDR with a period of reversing electrodes at 3 h. All the results demonstrated that the optimization of ED process is beneficial to the increasing of desalination rate as well as the decreasing of energy consumption in the “NF/EDR” integrated system, besides, it provided research basis and data support for the pilot-scale system of the “NF/EDR” integrated membrane process.

A specially designed electrodeionization (EDI) stack was used for deep softening from simulated aqueous solutions containing low concentrations of hardness ions. Characteristics of the current–voltage (I–V) and resistance–voltage (R–V) curves of EDI and electrodialysis (ED) were compared at first, and then removal of Ca2+ ions was carried out in a continuous experiment under a constant applied voltage. In order to further investigate the abilities of EDI to remove hardness without chemical regeneration, performances of different processes were compared under various experimental conditions of applied voltage, concentrate flow rate, and feed solution composition. It was shown that with feed Ca2+ concentration of 5 mg dm−3, the dilute resistivity of 3.45 MΩ cm was obtained when under optimized operation conditions. It was also found that applied voltage and concentrate flow rate had remarkable impacts on the migration of Ca2+ ions. A dimensionless coefficient Kt was put forward to distinguish the “enhanced transfer” and “electoregeneration” mechanisms. It was found that scaling formation due to water dissociation on the membranes surface could be avoided under reasonable operation conditions. In addition, no significant influence on final hardness rejection was revealed with multi-species of feed solutions (Ca/Mg). The experimental results have demonstrated the feasibility of deep water softening by improved EDI technology.

•EDIR system was used for brackish water desalination to produce drinking water.•Appropriate applied voltages were chosen for the feed TDS of 2000–4000 mg L−1.•The operating polarity reversal period should be set to be 3.0 h or shorter.•The desalted product water meets quality standard for drinking water in China.•EDIR could be used to produce drinking water from brackish water with high TDS.Electrodeionization reversal (EDIR), which is electrodeionization using periodic changes of polarities, was examined in drinking water production from brackish water in this study. Using the characteristic curves of the EDIR process combined with the demineralization rate and energy consumption, the appropriate applied voltages were determined to be 11.0, 13.0 and 19.0 V for the feed total dissolved solids (TDS) of 2000, 3000 and 4000 mg L−1, respectively. The performance of the EDIR system, was affected by polarity reversal periods, which were determined to be 3.0 h or 2.0 h for different feed TDS. For feed water with TDS in the range of 2000–4000 mg L−1, varying voltage 11–19 V should be applied to ensure the demineralization rate to be not less than 90.0% at a constant water recovery of 75%, and the energy consumption was 1.04, 1.95 and 3.71 kWh m−3 for feed TDS of 2000, 3000 and 4000 mg L−1, respectively. The concentration of ions in dilute product water did not exceed the permissible WHO standards and taste quality of the product water was good. Thus, EDIR seems to be the economical desalination process for production of drinking water from brackish water.

•EDIR has been proposed for removal and recovery of Ni2 + from dilute solution.•The duration of polarity reversal should not be greater than 4 h.•Stepwise stream switching mode was employed to reduce Ni2 + loss.•Ni2 + removal efficiency was 97% and the concentrating factor was 79.2.The removal and recovery of Ni2 + from simulated electroplating rinse water by electrodeionization reversal (EDIR), i.e., electrodeionization using periodic changes in polarity, was studied. Based on the EDIR characteristic curves, the appropriate applied stack voltage was determined to be 30 V. The influence of the polarity reversal period on EDIR performance was examined. In addition, a stepwise stream switching mode was proposed to reduce Ni2 + loss. The experimental results showed that the duration of polarity reversal should not be greater than 4 h to prevent the formation of metal hydroxide precipitates. Additionally, the EDIR process with a polarity reversal period of 4 h and stepwise stream switching mode exhibited good separation performance, removing 97.0% of Ni2 + from the feed solution and simultaneously recovering these ions into a concentrate stream with a high concentration of 3961 mg·L− 1. The current efficiency was 32.6%, and the corresponding energy consumption to treat 1 m3 of water was 1.02 KW·h. Thus, EDIR has considerable potential for the recovery and reuse of heavy metal ions from electroplating rinse water.

•An energy-saving "NF/EDR" integrated membrane process for seawater desalination is proposed.•A kind of NF membrane with high desalination capacity is adopted.•A energy-saving NF system with ERD is performed.•A new kind of EDR device with multi-stage and multi-passages is proposed.In this study, an energy-saving nanofiltration/Reverse electrodialysis (NF/EDR) integrated membrane process for seawater desalination was proposed and about a total desalination removal of 99% could be obtained. The system energy consumption was < 2.15KWh/m [3], which is close to the most advanced level and the Total Dissolved Solids (TDS) of produced water was lower than 250 mg/L, the lowest can be 70---90 mg/L, demonstrating that the integrated system is an economically feasible and efficient desalination system. This paper is an important part of this system about the study on NF process, where a NF90-4040 membrane element with high desalination capacity was chosen by comparing the separation performance of the existing NF membranes at home and abroad, and the effects of operation pressure, feed concentration, stream temperature and feed flow on NF process were discussed in detail. The results showed that with the NF90-4040 membrane element, approximately 90% of the system desalination removal (SDR) was achieved, which was much higher than that of regular NF membranes. Furthermore, a NF system with an energy recovery device (ERD) was constructed. Compared with the NF system without ERD, the energy consumption of the ERD-based system was reduced by 46.4%. All the results are beneficial to the development of new integrated routes for seawater desalination based on high desalination capacity NF membrane, which is expected to play a significant role in the “NF/EDR” integrated membrane process.