The cover picture illustrates the use of switchable water, an aqueous solution with a CO2-switchable ionic strength, to expedite the settling of clay solids without making the process water permanently salty. In strip mining operations, the settling of fine solids such as clay particles from aqueous suspensions is often a time- and material-intensive process. In their Full paper on page 132, Horton and Jessop describe how calcium salts can be used to promote the settling of the solids; however, the liberated salts must then be desalinated before recycling. Using switchable water, the introduction of CO2 increases the ionic strength of the aqueous solution by reacting with an amine additive, thus promoting clay settling. The later removal of CO2 from the liberated water decreases the ionic strength, allowing the water to be recycled.
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