Polymer Process The Impact Of Sodium Aluminate Solution

The promotion of Gibbsite precipitation from caustic aluminatesolutions is always a hotspot in aluminum industry. As a method withgood application foreground, Al(OH)₃ precipitation from causticaluminate solutions with the addition of additives has importantadvantages such as simple operation and low cost, and is worthy offurther investigation.In this paper, the influence of a series of polymers with active groupsincluding polyalcohols, polyamide and polysaccharide on the seedprecipitation of sodium aluminate solution has been investigated.Experiments show that polymers with amido or hydroxyl group canobviously change the precipitation ratio and particle size distribution ofAl(OH)₃ products. The dosage and molecular mass of polymers can affectthe seed precipitation of sodium aluminate solution. The largestprecipitation ratio can be obtained with the addition of median molecularmass(10000) of polymer. Polyethylene glycol with low molecularmass(2000) can increase the particle size of Al(OH)₃ products.Polypropylene glycol can improve the seed precipitation of sodiumaluminate solution if the dosage is less than 0.308 g·L^-1. The largestprecipitation ratio can be obtained at the dosage of 5.13×10^-2 g·L^-1.Polypropylene glycol with the dosage of 0.308 g·L^-1 can increase theparticle size of Al(OH)₃ products. The more the dosage of polypropyleneglycol, the larger the mean particle diameter. The results of X-raydiffraction show that the crystal structure of Al(OH)₃ products remainsthe same with or without polymers.The effect of non-ionic surfactant-polypropylene glycol on the seedprecipitation of sodium aluminate solution has also been investigated.Experiments show that polypropylene glycol can improve the seedprecipitation of sodium aluminate solution and obviously increase thevolume percentage of +45μm particles of Al(OH)₃ products. The dosageof polypropylene glycol, experimental temperature, the size of seeds, themass ratio of seeds (Ks) and the molecular ratio(α_k) can obviously affect the seed precipitation of sodium aluminate solution. Low dosage ofadditive, high temperature, fine seeds, median mass ratio of seeds andlow molecular ratio are more propitious to the improvement of the seedprecipitation.The influence of a series of non-oily and oily polyalcohols on theprecipitation ratio of sodium aluminate solution and particle sizedistribution(PSD) of Al(OH)₃ products has been investigated.Experimental results indicate that seeds or sodium aluminate solution issensitive to polyalcohols with hydroxyl. All three polyalcohols canincrease the precipitation ratio and improve PSD of Al(OH)₃ products,especially by the addition of polyalcohols with one hydroxyl on each unit.The polar property of oil can affect obviously the seed precipitation.Nonpolar oil(paraffin wax) can enhance the precipitation process andenlarge the particle size with the addition of polyglycerol simultaneously,but polar oil(castor oil) can't. The dosage of paraffin wax has little effecton the precipitation ratio but large effect on PSD of Al(OH)₃ products.The more the dosage of paraffin wax, the larger the mean particlediameter.