Separation of carbon from fly ash using froth flotation

The unburned carbon content of fly ash from two different power stations was greatly reduced in two-stage laboratory flotation tests by employing a collector consisting of nonylphenol and either hexadecane or fuel oil together with methyl isobutinol (MIBC) as a frother. The tailings from the first stage were recleaned in the second stage. This method reduced the carbon content of fly ash from an initial level of 25.9% in one case and 16.5% in another case to a final level of 1-2% or less in the tailings while at the same time recovering 95% or more of the carbon in the floated material or concentrate. In most cases from 60 to 75% of the ash was rejected in the tailings. The results support a previous finding that a good collector for oxidized coal is a good collector for unburned carbon in fly ash. Furthermore, the results showed that much less collector was required to achieve a good separation of carbon from fly ash when MIBC was employed in conjunction with the mixed collector.