Aluminum trihydroxide deliquoring with anionic polymers

摘要

During the final stages of Al(OH)3 production, deliquoring the aluminum trihydroxide slurry of excess sodium ions in the form of caustic liquor is conventionally achieved by numerous water washes prior to drying the product. Addition of an effective amount of highly charged, high molecular weight anionic polymer flocculant to the aluminum trihydroxide slurry improves the filtration rate, i.e., increases the amount and rate of removal of caustic liquor from the slurry. Addition of the flocculant reduces the amount of washing necessary to remove sodium ions from the final cake and also provides higher cake solids which results in greater production per unit time and less expenditure of energy in the drying process. Anionic polymers derived from 80 to 100% of an anionic vinyl monomer such as acrylic acid and from 20 to 0% of a nonionic vinyl monomer such as acrylamide having molecular weights between 1.5 to 12.0x106 are useful in deliquoring aluminum trihydroxide slurries. Anionic polymer dosages of from about 150 to about 600 ppm may be used to treat 200 ml of about 5 to about 10% by weight of aluminum trihydroxide slurry. Higher dosages are required when aluminum trihydroxide concentrations are greater than 10% by weight.