Brief description of differences between European and Australian zeolites.
What is zeolite?
Zeolite is a crystalline hydrated alkali metal and rock alumosilicate. Its structure consists in having a spatial arrangement of atoms and creating pores of specific dimensions and shapes. These pores are sorted into micro, meso and macro pores. They have different size, density and arrangement. Solids, liquids and gases are collected in these pores.
Use of zeolites for treatment
When chlorine or salt (with chlorine generator) is used for water treatment (water sanitation), a characteristic chlorine odor is produced. Combinations of chlorine and ammonia coming into the pool from human sweat, body fat and urine can produce inorganic chloramines such as monochloramine (NH2CL), dichloramine (NHCl2) or trichloramine (NCl3). This causes skin irritation, eye irritation and odor.
To reduce the chlorine dosage, which can be reduced by up to 35% and the chlorine generator activation time from the salt, it is recommended to use a zeolite filter medium that eliminates odor and irritation. As a standard, the pools use discontinuous fast filters with a speed of about 40-50m3 / h and it is always necessary to use a dedicated type of zeolite with micropores (size 5 nm) and a hardness of about 7 Mohs as well as quartz sand or glass.
Often there are zeolites on the market that have a hardness of only 2-3 Mohs with macro pores (500 – 1000 nm), which are not intended for filtration in pools and are interchangeable !!!
Potable / process water
Zeolites have a significant presence in the treatment of drinking water due to their properties such as metal removal (except they are precipitated, which are removed by coagulation and flocculation). Zeolites do not affect pH and are a highly stable filter medium. Slow continuous filters are used in the treatment.
Properties of zeolite
Currently, at least 50 types of natural zeolites are known which differ diametrically from each other in terms of chemical composition and physical properties. Therefore, not all zeolites can be used for all types of water filtration applications.
For example, for slow continuous filters with a speed of about 3-10m3 / h for drinking water treatment, zeolites with a hardness of about 3 Mohs hardness scales can be used.
On the contrary, for fast discontinuous filters with a speed of about 40-50m3 / h, which are used for pool water filtration and it is necessary to use a specific type of zeolite ZeoPure from Australia, which reaches around 7 Mohs hardness scale.
Another important property of zeolites in water treatment is porosity and the associated pore size, which is divided into micro, meso and macro pores. Australian type zeolite, which has the only pore size of only about 5 nm can be due to its properties considered antibacterial !!!
For information, the size of the E-Coli bacterium is 500 nm in diameter.
The diversity of natural zeolites is very extensive and is divided according to the effective diameter of the input pores. The most common types of zeolites are Klinoptilolite, Analcim and Mordenite. The zeolite in the internal structure forms interconnected channels and cavities containing bound water molecules and alkali metal cations (K, Cs Na, Li) and alkaline rocks (Ca, Ba, Sr, Mg). In addition, zeolites are classified according to the size of the free volume. Broad-porous zeolites are sparse, while dense zeolites are narrowly porous. The size of the internal space is proportional to the value of adsorption capacity, ability to exchange ions, exchange cations into other cations and high adsorption of cations from ambient water containing ammonia and heavy metals.
These properties are used for example in water softening.
Distribution of zeolites according to pore size
Wide-porous – with pore size 50 – 1000 nm, internal volume 45% (European zeolite)
Medium-porous – with a pore size of 2-50 nm, an internal volume of 30-40% (US zeolite)
Narrow-porous – with a pore size of 0.2-2 nm, internal volume 30% (Australian zeolite) Antibacterial !!!
Distribution of zeolites according to adsorption
Physical adsorption: Several layers of adsorbate with a very high capacity and filtration efficiency of about 2 microns can be formed on the surface.
Chemical adsorption: Only one layer of adsorbate can form on the surface, which is very low due to the limited area.
Electrostatic adsorption: Molecular or ionic.
Ion exchange occurs between ions contained in water and zeolite, which bears a permanent negative charge in the case of natural and a positive charge in the case of a modified one. This leads to the binding of ions with opposite charges (protions). Protions can be exchanged for ions of the same charge from water.
The properties of zeolites, such as ion exchangers, are substances which carry functional groups on their surface and are dissociable. Dissociation of these functional groups releases simple ions, called counterions. The counter ions are bound to the zeolite bearing functional groups by not very strong bonds of opposite electrical charges and are exchangeable under appropriate conditions for other ions contained in the aqueous solution with which the zeolite is in contact. Preferably, ions having a higher charge density, a higher charge and the highest concentration in water are sorbed. The total capacity is the sum of all adsorbable ions on the inner and outer surface of the zeolites.
Zeolites (Ionexes) are divided into:
Cation exchangers (negative charge) in which a cation such as Na +, H + etc. is positively charged against the ion.
Anion exchangers (positive charge) in which an anion such as Cl-, OH-, etc. is negatively charged against the ions.
Ion exchange values
Ca2 + 0.8 – 0.98 mol.kg-1, Mg2 + 0.05 – 0.19 mol.kg-1, K + 0.20 – 0.50 mol.kg-1, Na + 0.01 – 0.20 mol.kg-1
Ammonium ion exchange: 1.050 Meg / 1 Kg,
Cation exchange: 1.470 Meg / 1 Kg
Total exchange capacity: 1,1– 1,7 mol.kg-1
Activation / modification of zeolites
Zeolite activation is performed by ZeoPure ZAS Zeolite Activation Solution to increase efficiency in the interior of the structure and change the surface charge on the surface of the zeolites. Natural extracted material has a negative charge, it contains water and particles of inorganic origin, which fill the interior space and thus reduce its capacity. Activation of zeolite by surfactants (surfactants) is performed to change the polarity from negative to positive charge. Modification of the zeolites by changing the surface tension and hydrophobization for pool water filtration is performed to increase the grease resistance and the adhesion of organic contaminants. Activation is recommended depending on the type and type of use. Thus, what is good for the adsorption of ammonium ions may not be suitable for other applications.
Without activation – the efficiency is only 40% compared to the activated ones
Acidification – eg HCl at the concentration 0,02 efficiency 79% and at 0,04 only 64%
Ion exchange – values vary by type
Surface surfactants – surface tension change. Efficiency can be up to 500% !!!
Regeneration / cleaning
The regeneration of zeolites is always carried out according to the type of application and in which environment they work. For example, a NaCl solution that is less effective than special regeneration solutions such as ZeoPure ZFC Zeolite Filter Cleaner has been used to regenerate zeolites used with n Na + or Cl-. Using special ZeoPure ZFC Zeolite Filter Cleaner solutions will significantly reduce regeneration time and increase the zeolite ion exchange efficiency by 10% to as much as 98% of the original capacity. It should also be taken into account that a higher concentration of regeneration solution may have a negative effect on the capacity.
Cleaning is carried out primarily in batch filtration, for example in swimming pools. In addition to standard regeneration to restore ionic adsorption capacity, contamination that has entered the filtered water circuit from human skin such as hair, skin, sunscreen grease, precipitated calcium carbonate and other inorganic and organic contaminants is also required.
The cleaning is carried out with active filtration and regeneration solutions such as ZeoPure ZFC Zeolite Filter Cleaner, which restores the ionic capacity and perfectly cleans the filter zeolite.
The cation exchangers used in the H + cycle are regenerated with HCl or H2SO4 (5 – 10%, ie 5 times the capacity)
The anion exchangers used in the OH-cycle are regenerated with NaOH (3 – 5%, ie 5 times the capacity)
The ion exchangers used in the Na + or Cl- cycle are regenerated by ZeoPure ZFC or NaCl (5-10%, ie 5 times the capacity)
The above-described use of zeolite for water treatment is a brief summary of the technical documentation of ZeoPure products, which can be found in full at www.zeopure.eu