Study On Electro-driven Membrane Processes For Desalination And Resource Utilization Of High-saline Brine

The total dissolved solid of high-saline brine is higher than 1 wt.%,which is characterized by extensive sources,complex components and distinct industry direction.With the rapid development of economy and society,the scientific disposal of high-saline brine has become a bottleneck problem related to the sustainable development of related industries and the healthy circulation of ecological environment.Therefore,recovery of dissolved resources in high-saline brine is of great practical significance to solve the problem of chemical resource shortage and water environmental pollution.And the strategies of efficient removal,utilization and high-value conversion of mixed inorganic salts in high-saline brine are the research hotspots and difficulties in related fields.Aiming at the technical problems of the sustainable disposal of high-saline brine in typical industries,this paper innovated and developed new electro-membrane processes and membrane integration technologies centering on the efficient resource utilization of inorganic salt,organic matter and water resources.Committed to providing new ideas and data support for the upgrading of zero liquid discharge（ZLD）and resource-based treatment technology of high-saline brine.The results observed mainly include the following three aspects:（1）Electrodialysis（ED）was introduced into the desalination unit of the ethylene glycol（EG）recovery system for combustible ice mining,to alleviate the energy-intensive investment of conventional thermal desalination process.First,the feasibility of ED for converting rich-EG into reusable EG resources was preliminarily explored in bench-scale experiments.Under the optimized operating parameters,including the applied voltage of 1 V per membrane cell and membrane surface velocity of 0.36 cm/s,the bench-scale ED process reached a 90%desalination ratio with 9.8 k Wh/m³ energy consumption and 0.58%EG leakage ratio when treating rich-EG solutions with 40 wt.%EG.Furthermore,a pilot-scale system was developed based on three-stage ED integrated process:when treating saline-EG solutions with 40 wt.%and 60 wt.%EG under 1.3 V per membrane cell,the three-stage pilot-scale ED process attained continuous desalted EG solution（lean-EG）with total dissolved solids of 2.55 g/L and9.22 g/L,and achieved 90%and 65%desalination ratios with energy consumptions of16.19 k Wh/m³ and 10.41 k Wh/m³,respectively.The lean-EG was concluded here to be usable for the concentration process in an MRU system and without the precipitation of salt crystals in the downstream equipment.Furthermore,by economic estimation,the costs were$3.82 or$3.30 per cubic of lean-EG.These results showed that ED could be considered as a prospective technology in HSEG desalination and thus provided a practical design scheme and data support for the large-scale actual application.（2）An integrated process system with electrodialysis metathesis（EDM）as the core was proposed towards the conversion and concentrate of scaling-prone brine（SPB）.By introducing Na Cl as the metathesis reagent,the nanofiltration reject brine was converted into high-concentrate liquid salts（HCLS,Na-type and Cl-type HCLS）,which provides an effective strategy for the ZLD and resource recovery of SPB.The study mainly includes:evaluating the concentrate performance of various ion exchange membranes（IEMs）;analyzing the feasibility and optimized process of two-stage feed-and-bleed EDM（FB-EDM）process.For the EDM process,the necessity of fixed ionic density and selective permeability within the IEMs is clarified.Meanwhile,it is found that thicker IEM has a weaker water permeability effect,and the advantages of semi-homogeneous Lh type IEMs were preferred.Moreover,a two-stage FB-EDM integrated process was developed to realize the deep recovery of ions from SPB.The optimized conditions included a V_D:V_C maintained at 2:1,the replenishment flow rate of 4 L/h,initial diluate compartment concentration ratios(C_D1:C_D2)of 1.5:1,and the voltages of 1st and 2nd stage EDM are 1.5 V and 1.2 V per membrane unit,respectively.The two-stage FB-EDM process operating under the optimized conditions:the 1st stage EDM can concentrate the Cl-type and Na-type salts to 213.5 g/L and 241.1 g/L,respectively;and for the 2nd stage EDM,the concentration of Cl-type and Na-type salts were 151.0 g/L and 168.1 g/L,respectively.Finally,199.1 g/L Cl-type and 224.4 g/L Na-type salts were obtained by blending the two-stage EDM overflow concentrate.Accordingly,the TDS of the feed solution was reduced from 84.0 g/L to 13.5 g/L with specific energy consumption of 0.67 k Wh/kg.The obtained diluate can be used to improve water recovery in seawater desalination,considering that the water quality is superior to natural seawater.In addition,based on the fact that the ionic product（IP）of Ca²⁺and SO₄^2-in two types of HCLS is much higher than the solubility product constant(K_SP)of Ca SO₄,the self-crystallization tendency of Ca²⁺and SO₄^2-was determined.On this basis,the parameters of the gradual resource recovery process of constant ions were optimized,and valuable inorganic products such as Ca SO₄·2H₂O and Mg（OH）₂ were obtained as expected.The two-stage FB-EDM integrated process has realized the resource recovery and ZLD of scaling-prone brine.（3）An integrated process of nanofiltration and EDM（SNF-EDM）has been attempted to prepare K₂SO₄ from sulfate-rich wastewater.In SNF units,concentrating of Na₂SO₄accompanied by the efficient separation of Cl^-and SO₄^2-were realized by diafiltration mode including preconcentration-continuous constant volume diafiltration-post concentration.Concentrate Na₂SO₄ solution with TDS of 53.0 g/L and purity of 96.7%was obtained under the optimized parameters（4/2preconcentration factor and 2.0 MPa operating pressure）.Then,a single-stage FB-EDM process was carried out for continuous conversion of Na₂SO₄ to K₂SO₄ with KCl as the metathesis reagent.The appropriate operating parameters are as follows:membrane unit voltage is 0.5 V and replenishment flow rate is 1.25 L/h.As a result,the purity of K₂SO₄ solution was 94.49%,and the corresponding specific energy consumption was0.58 k Wh/kg K₂SO₄.Finally,K₂SO₄ powder was prepared by simulated evaporation and crystallization,and the Cl^-content in the K₂SO₄ product met the qualified requirements of agricultural K₂SO₄ in the national standard.In conclusion,this paper innovatively designs practical and effective new electro-drive membrane process and integration systems against the background of ZLD and resource utilization of high-saline brine in typical industries,realizing efficient salt removal or recovery,which can provide guidance for the safe disposal of practical high-saline brine and has a good application prospect.