Valorization of acid mine drainage into potable water and valuable minerals through membrane distillation crystallization

• Published in: Separation and purification technology Vol. 334; p. 126084
• Main Authors: Nthunya, Lebea N., Pinier, Justine, Ali, Aamer, Quist-Jensen, Cejna, Richards, Heidi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 14.04.2024; Elsevier
• Series: Separation and Purification Technology
• Subjects: Acid mine drainage; Circular economy; Engineering Sciences; Membrane distillation crystallization; Mine tailings leachate; Resource recovery; Membrane distillation crystallization; Resource recovery; Circular economy; Acid mine drainage; Mine tailings leachate
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2023.126084

•Resource recovery from environmentally polluting acid mine drainage requires efficient processes.•Membrane distillation crystallization recovered water and mineral salts from mine tailing leachates.•To establish crystal morphology, size and distribution, the feed temperature was varied.•Orthorhombic and polymorphic structures were formed at low and high temperatures respectively.•The rate of crystal growth increased with temperature. Owing to the rise in population growth and demands for the current living standards, mineral and water resources are depleting at the alarming rate. Also, the mineral–water-energy nexus raises a concern of high-quality water and mineral production at low costs. Membrane distillation crystallization (MDC) has emerged as a promising technology capable of simultaneous water and mineral recovery from wastewater or industrially discharged brines. Herein, the MDC was evaluated for recovery of water and precious minerals from acid mine drainage discharged from the mine tailings. High quality fresh water with 99.9 % salt rejection and permeate flux of 2.32 kg·m−2·h−1 was recovered at 52 °C feed inlet temperature. Also, feed temperatures were varied to determine their impact on mineral crystal morphology, size distribution and growth rate. Predominantly recovered minerals were gypsum, manganese fluoride, potassium iron oxide, nickel oxide hydroxide, sodium sulphate and dihydrogen sulphate. Orthorhombic crystal structure of mineral salts was attained at low feed inlet temperature (34 °C). Higher feed inlet temperatures (i.e. 41° C and 52° C) promoted co-crystallization giving rise to orthorhombic polymorph structures. Narrow crystal size distribution was reported at low water recovery factor (initial growth) for all temperatures. However, the particle size distribution broadened as the recovery factor increased. The crystal sizes ranged from 3.91 ± 0.97 µm to 14.04 ± 3.31. Remarkably, crystal growth rate increased with an increase in feed inlet temperature. These findings open a research direction towards economic recovery of mineral and water to supplement the existing shortages. With a myriad of crystals obtained from the MDC process, an additional operational unit is required to selectively recover high economic minerals.