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Carboxyl Hydroxamic Acids

In order to solve the problem in alumina production, it is important to develop new collectors of direct flotation for improving the Al/Si(mass ratio of Al2O3 to SiO2)of diasporic bauxite in China In this paper, the synthesis of novel alkyl carboxyl hydroxamic acids and their flotation properties to diaspore, kaolinite and illite have been studied. The adsorption mechanism of the new collectors on the minerals has been investigated through adsorption amount, zeta potential, SEM and IR spectrum measurements.
Three carboxyl hydroxamic acids, CMCA, CDHA and CTHA were synthesized by reaction of hydroxylamine hydrochloride with relevant ester. The molecular structures of synthesized products have been identified by IR spectrum and element analysis.
The result of flotation tests for single minerals indicate that the collection ability of carboxyl hydroxamic acids for diaspore, kaolinite and illite is in the order of CTHA >CDHA>CMCA, the collecting ability and selectivity of CTHA are better than those of CDHA and CMCA. Using CTHA and CDHA as collector in the PH range of 5-9, diaspore have good flotation recovery; However, kaolinite and illite still keep a relatively low flotation recovery. At the dosage of 2×10-4 mol/L, both CDHA and CTHA show excellent collecting abilities for diaspore with the recoveries over 90%, but for kaolinite and illite the recoveries were less than 30%. Therefore, it is possible to separate the diaspore from such silicate minerals as kaolinite and illite using CTHA and CDHA as collector in the PH range of 5-9. So, CTHA may become a new type of selective collector for direct flotation to remove aluminosilicate minerals from bauxite. The results of separation of artificially mixed minerals present that the mass ratio of Al2O3 to SiO2was increased to a high level, and the recovery of Al2O3is more than 85%.
SEM (×10,000) shows that diaspore takes oval shape, kaolinite and illite takes irregular appearance. The adsorption measurement indicates that the adsorption on diaspore is lager than that on kaolinite and illite, which is generally consistent with the flotation tests. Zeta potential and IR spectrum measurements approve that the interaction of the collector on the diaspre surface is mainly a chemical adsorption, while the adsorption on kaolinite and illite is mainly dominated by physical adsorption. The chemical adsorption of chelator is ion on diaspore may take place through-COOH,-NHOH and the Al3+ on the surface of mineral to form double rings.