Remediation of Metal-Bearing Aqueous Waste Streams via Direct Carbonation

Direct carbonation using liquid carbon dioxide can be used for the remediation of aqueous streams or slurries while sequestering carbon dioxide in the form of metal carbonates. Carbonic acid (pH = 2.9), which formed when the aqueous phase was contacted with excess liquid carbon dioxide at ambient temperature (295 K) and elevated pressure (6.89 MPa), reacted with the metal cations to form metal carbonates in the agitated vessel. These metal carbonates precipitated out of solution as the pH returned to neutral when the system was depressurized. Electric arc furnace K061 dust, red mud from the Bayer process of alumina manufacture, and metal-bearing wastewater streams were amenable to this treatment. The treatment of a K061-dust slurry from a steel plant was semi-continuous. The dust particles were retained in the high-pressure reaction vessel as fresh water was continuously injected and high-pressure, metal carbonate-bearing water was withdrawn. The water residence time in the reactor was 12 min. About 30% o...