Negative effects of dissolved organic compounds on settling performance of goethite in Bayer red mud

Goethite, a typical iron-containing monomineral in red mud, was synthesized under the simulated Bayer digestion condition during the alumina production. The effects of dissolved organic compounds including sodium formate, sodium acetate, sodium oxalate, sodium salicylate and disodium phthalate on the settling performance of goethite slurries were studied. The settling performance of the slurries was also investigated with the addition of self-made hydroxamated polyacrylamide flocculant （HCPAM）. The adsorption mechanism of dissolved organic compounds on the goethite surfaces was studied by FT-IR and XPS, respectively. The results show that the addition of organic compounds lowers the settling performance of the slurries and a deterioration in settling performance is observed in the order of sodium oxalate 〉 sodium salicylate （~ disodium phthalate） 〉 sodium formate 〉 sodium acetate. Moreover, HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the goethite slurries, but it can only partially improve the settling performance of the goethite slurries containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that these organic compounds are chemically adsorbed on the goethite surface.

Synthesis of modified polyacrylamide with high content of hydroxamate groups and settling performance of red mud

Hydroxamated polyacrylamide（HPAM） was synthesized from polyacrylamide（PAM） with high relative molecular mass under the optimum reaction conditions（p H 12 and a molar ratio of hydroxylamine to amide groups of 1.5 at 50 ℃for 12 h）. The hydroxamate groups of HPAM were verified by Fourier transform infrared spectrum（FT-IR）. 46%（molar fration） hydroxamate groups and 23%（molar fraction） carbonyl groups on HPAM were determined by conductometric titration combined with Kjeldahl＇s microanalysis method. The settling performance achieved at different flocculant dosages was investigated with high goethite-containing red mud slurry of simulated Bayer process synthesized in laboratory. It turns out that the settling performance of high goethite-containing red mud was better with HPAM. The average settling rate of red mud in the first 5 min and the turbidity of supernatant after settling for 30 min are 2.36 m/h and 507 NTU, respectively, at a flocculant dosage of 120 g/t, which is similar to that achieved with Hx-600.

Effects of intense magnetic field on digestion and settling performances of bauxite

The effects of magnetic field intensity, roasting temperature and roasting time on digestion rate and settling performance of bauxite with different iron contents were investigated systematically. The results indicate that such magnetic treatment can profoundly change the microstructure and digestion performance of bauxite. For the two samples carrying different iron contents, phase transformation of the aluminum oxide phase proceeds faster in the high iron bauxite than the low one. The optimal pretreatment conditions of low iron bauxite are roasting temperature 550 ℃ and magnetic field intensity 6 T, while for high iron bauxite are 500 ℃ and 9 T. The digestion rate of alumina can reach 95% and 92% at digestion temperature of 190 ℃ and 250 ℃. The settling performances of roasted ore by intense magnetic field after digestion are enhanced through pretreatment.

Negative effect of dissolved organic compounds on settling behavior of synthetic monominerals in red mud

Hydration grossular and hematite monominerals were synthesized. The effects of dissolved organic compounds(including sodium formate, sodium acetate, sodium oxalate, sodium salicylate or disodium phthalate) on the settling performance of hydration grossular or hematite slurries were studied. The settling of the slurries was also investigated with the addition of sodium polyacrylate(PAAS) or hydroxamated polyacrylamide flocculant(HCPAM). The adsorption mechanism of organic compounds on monominerals surfaces was studied by FT-IR and XPS, respectively. A deterioration in settling is observed in order of disodium phthalate>sodium salicylate>sodium oxalate>sodium formate(or sodium acetate). Moreover, PAAS can efficiently eliminate the negative effects of organic compounds on the settling performance of the hydration grossular slurry. HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the hematite slurry, but it only partially improves the settling performance of hematite slurry containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that organic compounds are physically adsorbed on hydration grossular surface, and chemisorptions of organic compounds occur on hematite surface with a bidentate chelating complex.