Before to Select Poly Aluminium Chloride, we should understand the formula chain, in the the general formula (Aln(OH)mCl(3n-m))x and have a polymeric structure,totally soluble in water.
The length of the polymerised chain, molecular weight and number of ionic charges is determined by the degree of polymerisation. On hydrolysis, various mono- and polymeric species are formed, with Al13O4(OH)24 7+ being a particularly important cation. A less predominant species is Al8(OH)204+
These highly polymerised coagulants include the following:
- Polyaluminium chloride (PACl, n=2 and m=3),
- Aluminium chlorohydrate (ACH, n=2 and m=5), and
- Polyaluminium chlorohydrate (PACH): similar to ACH.
In practice, there is little difference between the performance of ACH and PACl in water treatment applications, even though ACH is more hydrated.
An important property of polyaluminium coagulants is their basicity. This is the ratio of hydroxyl to aluminium ions in the hydrated complex and in general the higher the basicity, the lower will be the consumption of alkalinity in the treatment process and hence impact on pH.
Note:
Basicity varies from mfr to mfr, which is 44% to 82% w/w
Polyaluminium chloride solution (10% Al2O3) is stable for 4 to 5 months when stored at less than 50oC and is so ideal for bulk storage and dosing installations.
Advantage of Poly Aluminium Chloride over Alum