ALCHLOR PREMIUM Polyaluminium Chloride Solution
(≥ 23.5 wt% AI2O3) Chemical Name
Aluminium Chlorohydrate, Polyaluminium Chloride (83-85% basic). Also known as: Aluminium Hydroxy Chloride, Aluminium Chloride Hydroxide, dialuminium chloride pentahydroxide. Product Description
Coagulant used for potable water treatment and in pulp & paper processing. Requires much lower dosage rates than alternative alum treatments. Alchlor Premium is a much more cost-effective treatment solution than alternative alum-based methods with higher tolerances for variations in water quality. Product Uses
Specialist coagulant in the treatment of water and wastewater; some miscellaneous applications. Container Size(s)
20L Cubes (25 kg)
200L Drum (270kg net)
1000L IBC (1350kg net)
Bulk WEIGHT
1345 kg/tonne Technical Information
Please find below technical information on Alchlor Premium. This product was previously called Alchlor-AC and so is reffered to as such in the following text.
A Material Safety Data Sheet and Specification Sheet is also available for this product, please go back to download these. ALCHLOR-PREMIUM (previously ALCHLOR-AC)
Concentrated High Basicity Polyaluminium Chloride Solution General description Alchlor®-AC is a concentrated high performance aluminium-based coagulant solution that can be used for the clarification of both potable water and waste water. Alchlor®-AC contains aluminium at a typical concentration of 12.4% by weight, which is equivalent to 23.5% alumina (Al2O3).Alchlor®-AC can be described by the following simplified formula:Al2(OH)5ClAs the formula suggests, for every two aluminium atoms there are 5 hydroxide ions and one chloride ion. The two aluminium atoms carry a total positive charge of six units. The five hydroxide ions each have a negative charge of one unit. Hydroxide ions tend to neutralise acids, a property described as basicity. Because there are five basic hydroxide ions for every two aluminium ions, which account for six (positive) units of charge, Alchlor®-AC can be described as 5/6 basic or 83% basic aluminium chloride. The term "aluminium chlorohydrate" is normally understood to refer to solutions of this basicity. What are poly-aluminium chlorides?In solutions of poly-aluminium chloride (PAC), aluminium ions have formed into polymers consisting of clusters of ions bridged by oxygen atoms. These polymers only form in solutions of aluminium salts that have been partially neutralised by reaction with a base. As a general rule, the degree of polymerisation increases with the extent of neutralisation. Neutralisation confers basic properties on the solution, and hence the term "basic aluminium chlorides". Full neutralisation of an aluminium salt results ultimately in precipitation of aluminium hydroxide, with the general formula Al(OH)3, or Al2(OH)6. The simplified formula for Hardman Alchlor®-AC, which is Al2(OH)5Cl, suggests that the solution is 5/6 neutralised, or 5/6 basic, compared to aluminium hydroxide. Unlike aluminium hydroxide however it forms a stable solution in water. As it is highly basic, it is also highly polymerised.On the other hand, alum sulphate solution, which is highly acidic, is not polymerised to any extent. The solution consists of individual hydrated aluminium cations, designated Al3+(aq).The extent of neutralisation is described by the term "basicity", which is a measure of the number of hydroxide groups per aluminium, in comparison with the 100% value of three. Alchlor®-AC is said to have a basicity of 5/6, or 83%. Different grades of PAC solution may vary not only in their concentration but also in their basicity.According to the European standard for polyaluminium chlorides (BS EN 883:1997), a solution is defined as a basic aluminium chloride when it has an OH/Al mole ratio exceeding 1.05. This implies a basicity exceeding 35%. How does the polymerisation of PAC solutions relate to coagulation performance?When aluminium or iron salts act as coagulants, they undergo a series of reactions with water (termed hydrolysis), ultimately forming metal hydroxides, which settle out, resulting in removal of suspended solids. When a non-polymerised aluminium salt such as alum sulphate is applied to the water to be treated, the operative chemical species are formed in situ, during or after mixing, by reaction with water (which is called hydrolysis). The hydrated Al3+ cation is not involved (and neither is the sulphate ion). The operative chemical species are believed to be various polymeric forms of aluminium, similar in fact to the species present in solutions of PAC. For this reason, PAC solutions are sometimes termed "pre-hydrolysed" aluminium salts. The fact that the operative coagulant species are already partially formed in PAC solutions has a lot to do with their superior coagulation properties. Coagulation and flocculation processesIn water treatment, the purpose of coagulation is to remove suspended matter from water in order to bring about clarification. Coagulation is a chemical and physical process whereby colloidal particles, which normal carry a negative surface charge, collide with positively charged ions formed by the reaction of coagulant chemicals such as Alchlor®-AC with water. The neutralisation of the surface charge on the particles results in their cohesion and agglomeration into larger particles, which then settle rapidly.During the process of coagulation, aluminium-based coagulants such as Alchlor®-AC hydrolyse to form a precipitate of aluminium hydroxide, which appears as spongy gelatinous masses that are frequently referred to as "floc". This floc has a very high surface area that can act to absorb or entrap bacteria, protozoa and other turbidity-causing particles. Since colour-causing humic substances react with most coagulants, removal of natural colour is another desirable outcome of the coagulation process. Emulsion breaking and separation of emulsified oil and grease from wash water are also achievable.Flocculation is a term often used interchangeably with coagulation. According to the handbook of the United States AWWA, entitled Water Quality and Treatment (4th Edition), flocculation is the second stage in the overall coagulatiuon process in which "physical processes transform smaller particles into larger aggregates or "flocs".Coagulation is normally accomplished in three stages as follows:
A. An initial rapid or turbulent mixing of the Alchlor®-AC with the raw water or waste water. This provides contact
between the particles causing the turbidity and the Alchlor®-AC (coagulant), thereby neutralising opposite
charges.
B. A period of slow, more gentle agitation, allowing the agglomerates (the "floc") to grow and entrap more suspended
matter.
C. A further period of little or no agitation to allow the agglomerates to settle out of suspension or to be elevated to
the surface by dissolved air flotation When is clarification required?All water supplied to potable water systems should be both clarified and disinfected. Removal of colour is also advisable, both for aesthetic purposes and because colour is generally caused by the presence of natural organic matter (NOM), which tends to react with disinfection agents to generate toxic disinfection by-products (DBPs). In the USA, the EPA has imposed limits on the level of DBPs, which is compelling water treatment plant operators to set more stringent targets for the removal of organic matter prior to disinfection. The DPBs of most concern to US regulators are trihalomethanes such as chloroform, which can form by the reaction of chlorine-based disinfectants with NOM. At the same time, the US EPA has tightened the requirements for filtered water turbidity to a maximum of 0.1 NTU, with the primary aim of reducing the level of water-born pathogens such as cryptosporidium. These two requirements impose greater reliance on the performance of coagulants, and in many cases PAC-type coagulants are allowing operators to meet the tighter performance criteria.Non-potable water systems may also require clarification to remove suspended solids and other sources of turbidity and colour. Coagulants can be applied to the following problems that may affect non-potable water systems:
i. Inadequate water supply throughout the system due to progressive plugging and fouling of supply and process
lines.
ii. Fouling and inefficient operation of ion exchange equipment such as softeners and deionisers.
iii. Inefficient heat transfer in process cooling water systems leading to increasing inefficiency and ultimate failure.
iv. High maintenance costs for cleaning, repair and replacement of supply lines, seals, valves and pumps and other
equipment in the water reticulation system.
v. Rejection or downgrading of product due to staining or off-colour appearance.
vi. Increased water usage and loss of environmental efficiency associated with the above effects. What causes turbidity?Natural turbidity is usually associated with surface waters in the form of colloidal clay particles, suspended and mobilised by the erosive action of water on soils and rocks. The particles that remain suspended are typically less than 2 micrometers (microns) in diameter. Other fine suspended particles may originate from man-made causes and can include bacteria, protozoa and organic matter. How can the agglomerated solids be removed?Most turbidity once treated by agglomeration can be removed from waters by settlement or entrapment in filtration processes. This may be assisted by treatment with a suitable polyelectrolyte.Basic settlers have the disadvantage of being large and requiring significant retention times. In settlers, sludge is usually removed from the base of the settler while the clarified waters are generally taken as the overflows. Retention times can be reduced by the use of alternative technology, such as in the form of membrane filters or sand filters. Advantages of Alchlor®-AC:IMPROVED PERFORMANCE: depending on the application, Alchlor®-AC is frequently shown to exhibit improved performance over alum at equivalent dose rates in terms of removal of colour, turbidity, particle count or organic matter. This may allow the use of lower dose rates, leading to lower sludge volumes.TRANSPORT: Alchlor®-AC is readily transported in 200 litre plastic Mauser drums, in 1000 litre bulki-boxes or in bulk tankers of up to 20,000 litres. Because Alchlor®-AC typically contains 23.5% w/w alumina equivalent, it offers some cost saving over the traditional alum sulphate coagulant, which typically contains 7.5% w/w alumina equivalent and as a result requires the cartage of larger volumes of water.LOW CORROSIVITY: unlike alum sulphate, iron-based coagulants and medium basicity polyaluminium chlorides, Alchlor®-AC is classified as non-corrosive under the Australian Dangerous Goods code, making it cheaper to store and transport.STABILITY: solutions of Alchlor®-AC are stable for at least five years, unlike sulphate-containing poly-aluminium chlorides and solutions of sodium aluminate.LOW pH EFFECT: aluminium and iron-based coagulants form metal hydroxides when they coagulate. In effect they are fully hydrolysing to become 100% hydroxylated, releasing a hydrogen ion for each hydroxyl group (OH) acquired. This in turns leads to a fall in the pH of the water being treated as it becomes more acidic. Since Alchlor®-AC is already 83% hydroxylated (while alum sulphate has near-zero hydroxylation), the magnitude of this pH drop is significantly lower. The equations below depict this effect in terms of the overall hydrolysis reaction of each coagulant:ALUM SULPHATE:2Al3+ + 6H2O → 2Al(OH)3 + 6H+Alchlor®-AC:[Al2(OH)5]+ + H2O → 2Al(OH)3 + H+For example, water with zero alkalinity and a pH of 7.0, when treated with alum sulphate at a dose of 10mg/L alumina would have a final pH of 3.2 at full hydrolysis. In contrast, when treated with Alchlor®-AC at the same alumina dose rate, the final pH would be 4.0. The table below compares the pH effect of the two coagulants on zero-alkalinity water at three different dose rates: | Coagulant | Basicity
(%) | Dosage (mg/L as alumina) | pH after
hydrolysis | | Alum sulphate: | 0.0 | 10 mg/L
20 mg/L
50 mg/L | 3.2
2.9
2.5 | Hardman
Alchlor®-AC | 83.3 | 10 mg/L
20 mg/L
50 mg/L | 4.0
3.7
3.3 |
In reality most waters are alkaline to some degree and will counteract the drop in pH so that the magnitude of the drop is lower. Nevertheless most waters when treated with alum sulphate require some degree of pH adjustment before treatment in order to counteract the fall in pH. When treated with Alchlor®-AC at the equivalent alumina dose rate they will require either less pH adjustment or none at all.The initial pH and alkalinity of the water are of course important variables that can be adjusted for the purpose of fine-tuning coagulant performanceABSENCE OF SULPHATES: Alchlor®-AC is a sulphate-free coagulant, an important feature in waste systems and other high-dose applications. In waste systems, reducing conditions can give rise to sulphides and associated odour problems while sulphates can cause corrosion of concrete pipes.ABSENCE OF COLOUR: unlike iron-based coagulants, Alchlor®-AC is colourless and does not generate coloured compounds with some organic wastes.DIRECT FILTRATION AND MEMBRANE FILTRATION: in some applications where there is a need to filter immediately after coagulation, Alchlor®-AC has been shown to generate flocs that are more easily filtered, resulting in less frequent back-washing. In cases where polyelectrolyte is used to assist in floc formation, this may allow for the use of less polyelectrolyte, leading to extended filter runs, ultimately resulting in reduced operational costs.CALCULATION OF ALCHLOR®-AC dOSE RATESThe table below is based on the following values for Alchlor®-AC solution:Total aluminium as % w/w Al2O3 = 23.5
Density = 1.33 g/mL | Intended dose rate(mg/L of Al2O3) | Weight to add grams), per 1000 litres of water | Volume to add (mL), per 1000 litres of water | | 5 | 21.3 | 16.0 | | 10 | 42.6 | 32.0 | | 20 | 85.1 | 64.0 | | 30 | 128 | 96.0 | | 40 | 170 | 128 | | 50 | 213 | 160 | | 60 | 255 | 192 | | 70 | 298 | 224 | | 80 | 340 | 256 | | 90 | 383 | 288 | | 100 | 426 | 320 |
The above values are typical for Alchlor®-AC and are adequate for the majority of applications. If more precise dosing is desired then, providing the precise concentration and density are known, a more accurate dosage can be calculated as follows:Weight of coagulant to add (grams) =(volume, litres) ´ (dose rate, mg/L Al2O3)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
10 ´ (% w/w Al2O3 in coagulant)Volume of coagulant to add (millilitres) =(volume, in litres) ´ (dose rate, mg/L Al2O3)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
10 ´ (density, g/mL) ´ (%Al2O3 in coagulant)In the above equations, "volume" refers to the volume of water to be treated while "density" refers to the density of the coagulant solution.For example, when treating with Alchlor®-AC with a concentration of 23.6% Al2O3 and a density of 1.332 g/mL, you would require 424 grams, or 318 mL, to treat 5000 litres of water at a dose rate of 20 mg/L Al2O3. Divide weight by density to obtain volume. Most certificates of analysis give specific gravity (SG) rather than density. SG is a good approximation of density in g/mL. For reasonably accurate conversion, subtract 0.002 SG units from the SG to obtain density (as measured in air). DISCLAIMER: The information and suggestions presented herein are not intended to be exhaustive, but do represent the best information available to the company and believed to be accurate. However no warranty of performance is expressed or implied. |
