A novel green process for the synthesis of high-whiteness and ultrafine aluminum hydroxide powder from secondary aluminum dross

Secondary aluminum dross (SAD) is a dangerous pollutant as well as a valuable resource. About 95% SAD is disposed by stockpiling on the spot due to its complex composition and technical limitations, causing severe ecological damage and public health threat. A novel green process was developed herein for the preparation of high-whiteness and ultrafine Al(OH)3 from SAD. The SAD mixed with Na2CO3 and CaO was dry molded and roasted, then the Al and Na elements were efficiently extracted to produce a high-value product. The phase transition path and toxic element transfer behavior of the roasting and leaching processes were investigated by thermodynamic analysis, X-ray diffraction analysis, X-ray fluorescence spectroscopy, scanning electron microscopy, and chemical analysis. The recovery of Al and Na reached 95.12% and 97.33%, respectively, under the optimum conditions (roasting temperature of 1150 °C, Na2CO3/SAD mass ratio of 80%, CaO/SAD mass ratio of 24%, and roasting time of 1 h). The removal rates of Cl, N, and soluble F in the roasting product were 95.38%, 98.68%, and 98.57%, respectively. The test results showed a purity of 99.17%, a whiteness of 98.1 and an average volume particle size D(4, 3) of 2.053 μm for the prepared high-whiteness and ultrafine Al(OH)3 powder with uniform powder morphology. A cost analysis based on laboratory-scale data and market price indicates that a net profit of $431.6 can be obtained by recycling one ton SAD. The detoxification of SAD and the valuable Al element extraction can be achieved effectively by the green process.