High-performance PAC 9 HB for drinking water
To get good results in drinking water treatment, low aluminium-content and high basicity PAC 9%-10% Al2O3 content is employed.
Usually, PAC 9%-10% Al2O3 is produced by simple dilution of PAC 18% Al2O3, adding a basifier like Na2CO3, in order to reach a final basicity of 58 - 70%.
These products and similar formulations release about 200 ppb aluminium ions in the treated water and have a limited stability during the time.
Some equipment manufacturers supply complete plants for production of high-performance PAC 9HB, obtained by reaction of PAC 18% with aluminium sulphate and with two different types of basifier.
The reaction is carried out at room conditions without formation of solid residues, as common for other commercial processes which require a filtration. The stability to storage is very good and pH range is 2-3.
Basing on the know-how, the final product from plants is a Poly Aluminium Chloro Hydroxy Sulphate { Al2 (OH)x Cly (SO4)(6-x-y)/2 } 9% Al2O3, adjustable 60-68 basicity, containing a second basifier as sequestering agent.
This sequestering agent considerably improves the characteristics of the polymer, increasing the coagulation and flocculation velocity, even in case of low turbidity and low temperature. Moreover, the sequestering agent increases the storage stability of the final product.
The polymer hydrolyzes completely in treated water, leaving low residual aluminium content, less than 100 ppb with a dosage of 20 ppm, whereas standard PAC 9-10% HB leaves approx. 200 ppb aluminium ions. PAC 9HB forms large flakes which easily sediment, reducing the backwashing of sand filters and decanters.
In PAC 9HB plants, the basicity value for the output product is adjusted via software control system. In this way, it is possible to correct the working recipe of the plant according to the different physic-chemical characteristics of the raw materials used in the different batches, in order to obtain the same value of final basicity.
Keywords: PAC, Poly aluminum Chloride, poly aluminium chloride, Polyaluminum Chloride, PACL, Coagulant
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