Concentrating Aqueous Solution of Sulfuric Acid and Phosphoric Acid by Multiple-Effect Membrane Distillation

Multiple-effect membrane distillation(MEMD) was used to concentrate dilute aqueous solution of sulfuric acid or phosphoric acid by using self-made membrane module containing both micropous hydrophobic hollow fibers and dense-wall hollow fibers.Effects of heated feed-in temperature,feed-in flow rate and feed-in concentration on the MEMD performance were experimentally investigated.The experimental results demonstrated that permeation flux and performance ratio increased with the increase of heated feed-in temperature;permeation flux increased with the increase of feed-in flow rate,while performance ratio decreased at the same time;permeation flux and performance ratio decreased with the increase of feed-in concentration.Compared with phosphoric acid,the effects of the concentration of sulfuric acid on the performance of MEMD process were more evident.The maximum permeation flux and performance ratio were 5.3 L/(m2·h) and 11.5,respectively.Aqueous solution of sulfuric acid or phosphoric acid of 2 wt% could be concentrated to 40 wt% or above,while the electrical conductivity of the permeate was still less than 200 μS/cm.By using two AGMD modules,a long-term operational stability of the MEMD process was investigated using aqueous solution of 10% sulfuric acid solution as feed.The MEMD process showed excellent operation stability in a long-term test lasting for 30 days.