Evaluation of Pressure Retarded Osmosis for Energy Generation from Mine Water

This study examines the application of mining effluents as feed solutions in a bench scale pressure retarded osmosis (PRO) system for energy generation and the prospect of water recycling or safe discharge to the environment. Effluents were characterized and pretreated by ultrafiltration (UF) and nanofiltration (NF) prior to PRO. The PRO process was then conducted over 6 h in a cross flow flat plate cell with an effective membrane area of 34 cm2, a hydraulic pressure of 12.4 bar and a 3M ammonium carbonate (NH4)2CO3 as draw solution. Effluent 1 contained ions such as Cl− (539 mg/L), NO3− (585 mg/L), SO42− (3000 mg/L), Na+ (560 mg/L), and Mg2+ (656 mg/L), with a total dissolved solids (TDS) concentration of 5400 mg/L, chemical oxygen demand (COD) of 136 mg/L, total organic carbon (TOC) concentration of 3.5 mg/L, and acidic pH of 3.8, while effluent 2 was highly dominated by Cl− (32,100 mg/L), NO3− (9720 mg/L), SO42− (6512 mg/L), Na+ (14,306 mg/L), and Mg2+ (5336 mg/L), had a TDS concentration of 73,315 mg/L, COD of 8100 mg/L, TOC concentration of 10.2 mg/L, and pH of 7.4. These physiochemical properties indicated a significant potential of fouling and scaling which necessitated the appropriate pretreatments. It was shown that integrating UF and NF pretreatments was highly effective in refining the quality of effluents with a significant removal efficiency of above 90% for ions and heavy metals by NF, led to fouling mitigation, higher and more stable power density as well as potential water reuse or safe environmental discharge. The achieved water fluxes and power densities were 54 L/m2h and 18.6 W/m2, for effluent 1, and 38 L/m2h and 13 W/m2, for effluent 2, respectively. The outcome of this study is applicable for the mining sector especially in remote areas with the potential for water and energy recoveries to contribute to more sustainable mining operations.