Synthesis Of Hydroxamated Flocculants And The Effect Of The Flocculants On Red Mud Settlement And Separation

Abstract:Flocculants of synthetic polymer have played an important role in red mud settlement and separation process. The hydroxamated flocculants were commonly considered that have better performance on red mud settlement currently in the industry. Although some foreign companies have flocculants of this kind for sale, the price is expensive. Most of our research and exploitation on such flocculants have been still at the laboratory stage. Reports of literatures and patents on the synthetic conditions of the hydroxamated flocculants varied and a lot of technical information was kept under wraps.The present research situation of the hydroxamated flocculants used in red mud settlement at home and abroad was reviewed in this paper. Two types of hydroxamated flocculants were prepared through nucleophilic substitution reaction of high molecular weight polyacrylic acid and polyacrylamide as raw materials respectively with hydroxylamine:hydroxamated polyacrylic acid (HPAA) and hydroxamated polyacrylamide (HPAM). The synthetic experimental parameters of the two reactions were systematically studied, such as reaction temperature, time, pH and the reactant ratio. The optimum experimental parameters were obtained:(1)1,4-Dioxane used as the solvent, polyacrylic acid was activated by N, N’-carbonyldiimidazole at100℃for5h and then hydroxylamine hydrochloride was added at40℃and reacted for24hours. The contents of hydroxamic acid groups in the obtained products can be up to57%.(2) Ethanol used as the medium, polyacrylamide and hydroxylamine hydrochloride were heterogeneous reacted for12h at50-60℃, pH>12, the reactant ratio of2.0(the molar ratio of hydroxylamine and the amide groups),46%of the amide groups were transformed to hydroxamic acid groups.The presence of hydroxamic acid groups in the products was confirmed by color reaction with FeCl3and FT-IR spectrum. The contents of the hydroxamic acid groups were determined by Kjeldahl Method or Conductometric Titration Method. The products’flocculating and settling performance on red mud from digestion of the bauxite by Bayer process in laboratory which contains high content of goethite were tested.The impacts of the flocculants’added amounts, molecular weight and contents of hydroxamic acid groups on red mud settling effect were studied. It was found that sodium polyacrylate, polyacrylamide and foreign ALCLAR665and Nalco9779have poor settling performance. However, both of the two types of the synthetic flocculants have good performances on red mud settlement and separation. The high molecular weight HPAM with intrinsic viscosity of1100mL/g has an excellent performance:when the flocculants was added with120ppm dosage, the red mud settling velocity was8.6m/h and the supernatant turbidity was537NTU which was almost the same results compared to Hx-600commercial flocculants of Cytec company with60ppm dosage.