PAC - used as primary coagulant aid

PAC - used as primary coagulant aid

PAC - used as primary coagulant aid

Polyaluminum Chloride (PAC) is one of the most efficient water treatment chemicals utilized today.   It is widely used in both potable water and wastewater treatment because it provides high coagulation efficiency and it has the widest pH and temperature application ranges compared to other water treatment chemicals. This high efficiency provides for increased plant capacity and lower operating costs.  PAC has very little effect on pH resulting in minimized need for pH adjustment chemicals, thus further reducing operating costs.  PAC is used in the papermaking industry to increase drainage rates in neutral and alkaline processes, as a retention aid, to increase sizing efficiency and to reduce cationic demand.

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 Cl6-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.

Technicians developed know-how and technologies for production plants of the following grades of PAC:
PAC 18%: mid-basicity liquid PAC, containing 17,5 ± 0,5% Al2O3, specific for waste waters and neutral sizing in paper making. It is used as primary coagulant aid for any clarifying/flocculation process relating to the treatment of surface or underground water and urban or industrial effluents.
PAC 18 is based on highly charged aluminium which results in lower dosage and therefore reduces sludge volume and pH adjustment demand. It also improves solids and/or phosphorous removal over conventional coagulants.
PAC 9% HB: high-basicity liquid PAC, containing 9 ± 0,5% Al2O3, specific for potable waters.
PAC 30%: mid-basicity powder form, containing 30 ± 0,5% Al2O3.

These products and similar formulations release about 200 ppb aluminium ions in the treated water and have a limited stability during the time.

Some expertised industries 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 our 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. 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 under 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.

PAC applications
Water treatment - The poly aluminium chloride (PAC) is used for settling of solid particles present into drinkable waters and for the flocculation of civil and industrial effluents. It has also a high antibactericide effect, due to the presence of chlorine into the product formula, and can be utilized for large range of pH and with higher turbidity.
Paper manufacture - The main features of PAC are its high Al2O3 content and polymeric nature, which give rise to products of hydrolysis characterized by a high molecular weight and a large number of positive electric charges able to interact with the cellulose fibers and size, optimizing the sizing phase and the retention of fibers.

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