Polyaluminium chioride (PAC), Aluminium chlorohydrate (ACH), Coagulants, Water Treatment

Alum (aluminium sulphate) was the most commonly used coagulant in Australian water treatment plants, low cost being its major attraction. Alum however, has a number of disadvantages: 

limited coagulation pH range: 5.5 to 6.5,

supplemental addition of alkalinity to the raw water is often required to achieve the optimum coagulation pH, particularly for soft, coloured surface waters that are common in Australia,residual aluminium levels in the treated water can often exceed acceptable limits, and alum floc produced is particularly fragile. This is especially important if a coagulant is required to maximise colour removal in a microfiltration-based water treatment process.

Alum reacts in water to produce aluminium hydroxide and as a by-product sulphuric acid is also formed. The metal hydroxide precipitates out of solution and entraps neutralized charged dirt particles (turbidity), as well as coagulating soluble colour and organics by adsorption.

The sulphuric acid produced reacts with alkalinity in the raw water to produce carbon dioxide, thus depressing the pH.

POLYALUMINIUM COAGULANTS

Recent years, a number of altemative aluminium-based coagulants have been developed for water treatment applications.

These compounds have the general formula (Al_n(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)₂₀ ⁴⁺.

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 PACI in water treatment applications, even though ACH is more hydrated.

Keywords: Water Treatment, PAC, Poly aluminum Chloride, poly aluminium chloride, Polyaluminum Chloride, PACL, Coagulant, Flocculant, Yellow PAC, Yellow polyaluminum chloride, White PAC, White polyaluminum chloride, PolyDADMAC, DADMAC, PDADMAC, Polydmdaac, polyelectrolyte

Please simply fill out the Inquiry form, or Email us to serve you today!