Application of freeze desalination for chromium (VI) removal from water

• High Cr(VI) removal efficiency with low water rejection can be obtained by freezing
• Freeze desalination is useful for Cr removal in a wide range of Cr concentrations
• Removal efficiency decreases with increasing salinity

Chromium (VI) is a highly toxic metal ion found in the priority list of pollutants, which is also often abundant in areas having low access to high-tech solutions for chromium (Cr) removal. This study was initiated to investigate the capacity of home-use refrigerators to generate fresh water free from Cr(VI) by melting ice produced from Cr(VI) polluted water. Simulated tap water samples as well as deionized water to which different concentrations of Cr(VI) were added were frozen in a closed freezer unit. The effects of initial concentration, time of ice nucleation, fraction of ice volume, and influence of co-occurring ions were evaluated in relation to the quality of the produced ice. The physicochemical characteristics of the produced ice cubes were also evaluated. A high total water recovery of up to 85% was achieved. Chromium removal ranged from 57.4 to 80% for simulated tap and from 93 to 97% for deionized water spiked with Cr. The energy consumption estimation basing form the refrigerator amounted to 0.076 kWh. Freeze desalination was found to be relatively viable desalination technology in terms of quality of water produced, easiness for safe water production, and amount of energy consumed, especially where high-tech solutions for Cr(VI) removal are not available.