Experimental study on the membrane distillation of highly mineralized mine water

Ji Qi,Jingfeng Li,Wei Bian,Shuqin Liu,Jiafeng Lv

doi:10.1007/s40789-021-00432-6

Abstract

Membrane distillation (MD) is a promising membrane separation technique used to treat industrial wastewater. When coupled with cheap heat sources, MD has significant economic advantages. Therefore, MD can be combined with solar energy to realize the large-scale and low-cost treatment of highly mineralized mine water in the western coal-producing region of China. In this study, highly mineralized mine water from the Ningdong area of China was subjected to vacuum MD (VMD) using polyvinylidene fluoride hollow-fiber membranes. The optimal operation parameters of VMD were determined by response surface optimization. Subsequently, the feasibility of VMD for treating highly mineralized mine water was explored. The fouling behavior observed during VMD was further investigated by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). Under the optimal parameters (pressure = − 0.08 MPa, temperature = 70 °C, and feed flow rate = 1.5 L/min), the maximum membrane flux was 8.85 kg/(m2 h), and the desalination rate was 99.7%. Membrane fouling could be divided into three stages: membrane wetting, crystallization, and fouling layer formation. Physical cleaning restored the flux and salt rejection rate to 94% and 97% of the initial values, respectively; however, the cleaning interval and cleaning efficiency decreased as the VMD run time increased. SEM–EDS analysis revealed that the reduction in flux was caused by the precipitation of CaCO3. The findings also demonstrated that the membrane wetting could be attributed to the formation of NaCl on the cross section and outer surface of the membrane. Overall, the results confirm the feasibility of MD for treating mine water and provide meaningful guidance for the industrial application of MD.

Highlights

The western region of China, which is the nation’s main coal-producing region, accounts for 77% of national coal output (Dazhao et al 2016; Limin et al 2019)
The fouling behavior observed during vacuum MD (VMD) was further investigated by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–Energy-dispersive X-ray spectroscopy (EDS))
The findings demonstrated that the membrane wetting could be attributed to the formation of NaCl on the cross section and outer surface of the membrane

Summary

Introduction

The western region of China, which is the nation’s main coal-producing region, accounts for 77% of national coal output (Dazhao et al 2016; Limin et al 2019). Water scarcity in the region accounts for only 7.9% of the Traditional thermal desalination requires a large amount of heat energy. The reverse osmosis treatment of mine water has several advantages in terms of wastewater quality, power consumption, desalination efficiency, and land use. The current state has put forward higher requirements for mine water treatment. New coal mines in some areas are required to achieve zero liquid discharge (Dazhao et al 2016). Elena et al (2014) combined solar heat with MD and conducted a long-term pilot study. Guillen et al (2013) used seawater for a series of dry/wet cycles to simulate intermittent MD operation, which proved that hydrophobic membrane has chemical stability and anti-drying performance in MD operation, and could reduce the wetting phenomenon of membrane

Objectives

Methods

Results