Separation and Recycling of Concentrated Heavy Metal Wastewater by Tube Membrane Distillation Integrated with Crystallization

• Main Authors: Xiang-Yang Lou, Zheng Xu, An-Ping Bai, Montserrat Resina-Gallego, Zhong-Guang Ji
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: Membranes
• Subjects: wastewater treatment; membrane distillation; crystallization; heavy metals; concentrated solutions; membrane fouling
• Online Access: https://www.mdpi.com/2077-0375/10/1/19

Tube membrane distillation (MD) integrated with a crystallization method is used in this study for the concurrent productions of pure water and salt crystals from concentrated single and mixed system solutions. The effects of concentrated Zn²⁺ and Ni²⁺ on performance in terms of membrane flux, permeate conductivity, crystal recovery rates, and crystal grades are investigated. Preferred crystallization and co-crystallization determinations were performed for mixed solutions. The results revealed that membrane fluxes remained at 2.61 kg·m^−2·h^−1 and showed a sharp decline until the saturation increased to 1.38. Water yield conductivity was below 10 μs·cm^−1. High concentrated zinc and nickel did not have a particular effect on the rejection of the membrane process. For the mixed solutions, membrane flux showed a sharp decrease due to the high saturation, while the conductivity of permeate remained below 10 μs·cm^−1 during the whole process. Co-crystallization has been proven to be a better method due to the existence of the SO₄^2− common-ion effect. Membrane fouling studies have suggested that the membrane has excellent resistance to fouling from highly concentrated solutions. The MD integrated with crystallization proves to be a promising technology for treating highly concentrated heavy metal solutions.