PAC is a flocculant of new concept, the specific properties of which derive from the action of its basic active constituent, namely Poly Aluminium Chloride.
This is a polynuclear complex of polymerised hydro-aluminium ions, with the following general formula: { Al2 (OH)n Cl 6-n }x
PAC is supplied in form of water solution or as powder, which facilitates the transport and storage operations and subsequent dosage of the reagent.
Consito developed know-how and technologies for production plants of the following grades of PAC:
To get good results in drinking water treatment, where polyelectrolytes must be avoided for their mutagenic property, low aluminium-content and high basicity PAC 9%-10% Al2O3 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.
CONSITO TECHNOLOGIES supplies 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 Consito know-how, the final product from our 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. Our PAC 9HB forms large flakes which easily sediment, reducing the backwashing of sand filters and decanters.
In our 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.
The PAC 18% production process lines in the batch etching reaction of alumina with an acqueous solution of hydrochloric acid.
The reaction takes place in a glass-lined reactor equipped with internal agitator. During reaction the reactor temperature is controlled and at end of reaction the reaction product is discharged into an holding tank.
The discharged product is maintained in agitation and non reacted alumina and insolubles are separated by filtration.
The clarified product is transferred into vessels where the product is taken to standard specification. To this scope water, hydrochloric acid, aluminium sulphate can be mixed into the product according to market specifications.
A venting system assures the collection of vent discharges for storage tanks and safety valves.
The liquid effluents, mainly acid waters, are collected into a holding tank from which they are recycled to the production plant.
Using sulphuric acid instead of hydrochloric acid, Aluminium sulphate solution (Alum) can be produced with the same process.
The PAC 9 HB, production process is obtained by reaction of PAC 18% with aluminum sulphate and a basifier, using a GFRP reactor and a mixer-mill of particular design.
The reaction is carried out at room conditions and production filtration is not required.
Specifications | PAC 18% | Alum 8% | PAC 9HB | |
---|---|---|---|---|
Appearance | clear liquid | Liquid | clear liquid | |
Density at 20°C | kg/dm3 | 1.35 | 1.20 | |
Viscosity at 20°C | Cst | 21.6 | 10-20 | |
Freezing point | °C | -20 | ||
pH at 20°C | N. | 0.8 - 0.12 | 2 - 3 | |
Al2O3 content | % | 18 | 8 | 9 |
Al2O3/Cl ratio | max | 3.3 - 3.5 |
Formulations, according to end user requirements, will be obtained by blending the basic product with other formula components.
Referred to 1 metric ton of finished product:
Feedstock & utilities | PAC 18% | Alum 8% | PAC 9HB | |
---|---|---|---|---|
Alumina Al2O3 58-62% | kg | 330 | 150 | |
HCl 31-33% | kg | 700 | ||
Sulphuric acid 98% | kg | 250 | ||
PAC 18% | kg | 480 | ||
Alum 8% | kg | 80 | ||
Basifier 100% | kg | 20 | ||
Steam | kg | 250 | 180 | |
Cooling water | m3 | 20 | 20 | |
Electric power | kWh | 40 | 40 | 20 |
Compressed air | Nm3 | 20 | 20 | 15 |