Pilot studies on circular economy solution for the coal mining sector

The coal mining sector is being particularly affected by the saline waste waters problem. One of the possible solutions is to use the effluents as the source of raw materials: demineralized water, salt, magnesium hydroxide. This paper presents the results obtained in a pilot plant of capacity of 400 L/h, which was in operation for 9 months in the "Boleslaw ' Smialy" coal mine in Laziska Gorne, Poland. The coal mine water was being pre-treated with ultrafiltration and decarbonization and subjected to a two-pass nanofiltration, which splits the feed into two streams: salt-rich permeate, and calcium- and magnesium-rich retentate, which can be used for recovery of magnesium hydroxide by either conventional precipitation or by CrIEM technology. The nanofiltration permeate was concentrated in a hybrid reverse osmosis-electrodialysis system, producing demineralized water and highly saline concentrate, which could be used as a feedstock for salt production by either thermal crystallization or eutectic freeze crystallization.