| 摘要 |
Utilization of a cationic polymer as a settling aid in the recovery of the aluminum hydroxide and an anionic polymer to dewater the aluminum hydroxide prior to redissolution not only improves the process of making basic aluminum compounds by speeding settling and improving filterability, but also unexpectedly yields a product that has superior effectiveness as a water treatment chemical. According to the invention, a dilute solution of alum is neutralized with a base to a pH below about 6.0, preferably below 5.5, to form a suspension of aluminum hydroxide. A cationic polymer is then added to the suspension to assist in the settling of the aluminum hydroxide. When settling is substantially complete, the solution is decanted from the aluminum hydroxide and an anionic polymer is added to dewater the aluminum hydroxide. The dewatered material is collected as a filter cake containing amorphous aluminum hydroxide, the cationic polymer and the anionic polymer. The filter cake formed in this manner can be combined with aluminum sulfate or other aluminum species to form basic aluminum complexes. Surprisingly, however, the basic aluminum compounds formed from the filter cake are more effective in the reduction of water turbidity than comparable basic aluminum compounds formed without the use of the cationic and anionic polymers.
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