How is PAC used in water treatment

Polyaluminum chloride (PAC)

PAC is a new concept flocculant whose special properties come from the active ingredient, namely polyaluminum chloride.
It is a polynuclear complex of polymerized hydroaluminum ions with the following formula: {Al2 (OH) n Cl 6-n} x
PAC is supplied as an aqueous solution or powder to simplify transport, storage and dosing of the reagent.

Consito has developed the know-how and technology for production systems of the following PAC grades:

  • PAC 18%: Liquid PAC with medium basicity, contains 17.5 ± 0.5% Al2O3, specifically for wastewater and neutral coating in paper production. It is used as the primary thickening agent in clarification / flocculation processes in surface water or lake water or urban and industrial wastewater.
    PAC 18 is based on highly charged aluminum, which requires a lower dosage and consequently reduces the sludge volume and the need to adjust the pH value. It also improves solids and / or phosphorus elimination compared to common thickeners.
  • PAC 9% HB: Liquid PAC with high basicity with 9 ± 0.5% Al2O3, specific for drinking water.
    PAC 9 is based on highly charged aluminum, which requires a lower dosage and consequently reduces the sludge volume and the need to adjust the pH value. It also improves solids and / or phosphorus elimination compared to common thickeners.
  • PAC 30%: Powder with medium basicity with 30 ± 0.5% Al2O3.

Our high-performance PAC 9 HB for drinking water

In order to achieve good results in drinking water treatment, whereby it is necessary to avoid polyelectrolytes due to their mutagenic properties, PAC 9% -10% Al is also used2O3 used with high basicity and low aluminum content.
Usually you get PAC 9% -10% Al2O3 simply from the dilution of PAC 18% Al2O3 with the addition of a base former such. B. Na2CO3 to obtain a final basicity of 58 ÷ 70%.
These products and similar formulations release approximately 200 ppb aluminum ions into the treated water and have limited stability over time.

CONSITO TECHNOLOGIES supplies complete systems for high-performance PAC 9HB production, which is obtained by reacting PAC 18% with aluminum sulphate and two different types of base formers.
The reaction takes place under ambient conditions without the formation of residual solids, as is usually the case with other processes that require filtering. The storage stability is optimal and the pH value varies from 2 to 3.

Based on the know-how of Consito, the end product of our systems is the polyhydroxy chlorine aluminum sulfate Al2 (OH) x Cly (SO4) 6- (x + y) / 2} 9% Al2O3, adjustable basicity 60 ÷ 68, with a second base former as complexing agent.

This complexing agent significantly improves the properties of the polymer, increases its coagulation and flocculation speed, even in the case of low turbidity and low temperature. The complexing agent also increases the shelf life of the end product.

The polymer completely hydrolyzes in treated water, leaving a low residual aluminum level, below 100 ppb at a dosage of 20 ppm, compared to PAC 9-10% HB standard which releases approximately 200 ppb aluminum ions. Our PAC 9HB forms large flakes that easily sediment and reduce the countercurrent washing of the sand filters and sedimentation vessels.

In our PAC 9HB systems, the basicity value for the starting product is regulated by control software. In this way it is possible to correct the plant recipe according to the different physico-chemical properties of the raw materials used in the different batches in order to obtain the same final basicity value.

Production process

The production process of the PAC 18% is based on the discontinuous etching of the alumina with the aqueous solution of hydrochloric acid.
The reaction takes place in an enamelled stirred tank with an integrated stirrer. During the process, the temperature of the stirred tank is kept under control and, at the end of the reaction, the product is drained into a tank provided for this purpose.
The discharged product continues to be stirred while the unreacted clay and the insoluble substances are separated by means of filtering.
The clarified product is conveyed into containers in which the product is brought to standard specifications. To do this, the product can be mixed with water, hydrochloric acid and - depending on the market specifications - aluminum sulfate.
A ventilation system ensures the collection of the releases from the storage tanks and safety valves.
The wastewater, especially the acidic one, is collected in an encapsulated container in order to be used again later in the production plant.

If sulfuric acid is used instead of hydrochloric acid, it is possible to produce an aluminum sulfate solution (alum) using the same process.

The production process of PAC 9HB is achieved thanks to the reaction of PAC 18% with aluminum sulfate and a base-forming agent with a GFRP stirred tank and a specially designed mixer-grinder.
The reaction takes place under ambient conditions and the product does not need to be filtered.