The Interaction Between Flocculants And Major Iron-containing Species Of Red Mud From The Simulated Bayer Process

In the Bayer process, the sediment separation of red mud is an essential operation of the alumina production. Because the red mud residue with small particles is quite difficult to be settled during the Bayer process, flocculants, which are ultrahigh molecular weight water soluble polymers, are often used to improve red mud settling rate and facilitate the solid-liquid separation. Hematite (a-FeO3) and goethite (a-FeOOH) are the most important mineral fractions of red mud, so it makes sense to improve the flocculation effect of flocculants in order to make high hematite-containing or goethite-containing red mud be efficiently settled.In this paper, a suitable amount of Al(OH)3, NaOH and synthetic hematite or goethite were taken to be digested under the simulated condition of the Bayer process and subsequently diluted with simulative Bayer red mud lotion, then the synthetic hematite or goethite suspension, whose concentration of alkali (Na2Ok) was120g·L-1with1.52of the caustic molar ratio (ak, NaOH to Al(OH)3), was obtained. The flocculation effect of self-made modified poly(acrylic acids) flocculants containing hydroxamic acid groups (abbreviated as HPAA) or commercial sodium polyacrylate (abbreviated as PAAS) on the synthetic hematite or goethite suspension (abbreviated as the hematite or goethite suspension) was studied. In this paper, a suitable amount of high-containing silicon and high goethite-containing bauxite were taken to be digested under the simulated condition of the Bayer process and subsequently diluted with simulative Bayer red mud lotion, then the red mud slurry was obtained. The flocculation effect of HPAA、PAAS、 Hx-600and HCPAM (self-made flocculants containing hydroxamic acid groups) on the red mud slurry was studied.(1) When HPAA flocculated the hematite or goethite suspension respectively,with the increase of the dosages of added flocculants, the average settling rate of the synthetic hematite or goethite suspension for the first1min or5min sped up, the concentrations of suspended solids in the supernatant decreased. It also could been found that there was generally a decrease in the average settling rate of the synthetic hematite or goethite suspension for the first1min or5min with increased solid content of the suspension. When the solid content of hematite or goethite of the suspension was50g·L-1with240g·t-1dosage of HPAA, HPAA had a better flocculation effect on the synthetic goethite suspension than that on the synthetic hematite suspension.The adsorption mechanism of HPAA on the surface of hematite or goethite was investigated by Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS). These results suggest that HPAA is adsorbed on the hematite or goethite surface by chemisorption, and it has a stronger adsorption on the goethite surface than that on the hematite surface.(2) When HPAA or PAAS flocculated the goethite suspension, with the increase of the dosages of added flocculants, the average settling rate of the synthetic goethite suspension for the first1min or5min sped up, the concentrations of suspended solids in the supernatant decreased. It also could been found that there was generally a decrease in the average settling rate of the synthetic goethite suspension for the first1min or5min with increased solid content of the suspension. When the solid content of goethite of the suspension was50g·L-1with240g·t-1dosage of HPAA or PASS, HPAA had a better flocculation effect on the synthetic goethite suspension than that of PAAS. The adsorption mechanism of HPAA or PAAS on the surface of goethite was investigated by Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS). These results suggest that HPAA or PAAS is adsorbed on the goethite surface by chemisorption, and a stronger adsorption of HPAA on the goethite surfaces happened than that of PAAS.(3) The experimental results show HPAA and HCPAM had a good flocculation effect on the red mud slurry. And the flocculation effect of HCPAM was better on this red mud slurry than that of HPAA、PAAS and Hx-600.