Methods of correcting the chemical composition of water
Water iron removal.
The iron in the water can come from two sources: from seams containing iron salts and from water pipes in aggressive waters. In the second case, do not iron out the water, but remove its aggressive ingredients, even before entering the water supply system.
Iron from mineral deposits can be in the form of acid carbonates, sulfates or create combinations with humic substances. Iron bound to organic substances is the hardest to remove, because humic compounds are a protective colloid that inhibits the iron precipitation process. The iron content in water ranges from 0.03-14 mg / l in groundwater, 0,7—8.8 in surface water. The method of water de-ironing is determined on the basis of preliminary laboratory tests.
Water de-ironing can be done by the method:
a) aeration and filtering,
b) liming, aeration and filtering,
d) koagulacji z alkalizacją.
In Polish brewing, the method of iron removal by aeration and filtering is commonly used. Water aeration leads to the oxidation of divalent to trivalent iron and to the partial removal of CO2 from the water, which further facilitates the process of iron oxidation and its flocculation in the form of Fe(OH)3. After aeration, the water is filtered using a filter filled with quartzite gravel of various granulation.
Alkalizing action of water (bicarbonate ions) can be reduced by increasing the non-carbonate hardness with the addition of calcium chloride.
Hardening the water with calcium chloride can be done, if the water has the following properties:
— węglanowa twardość wody przewyższa twardość niewęglanową, but to a slight degree,
- the production water contains sodium bicarbonate (NaHCO3). Where the water contains soda and must be used in the brewhouse, the addition of calcium chloride or gypsum removes the harmful effects of soda.
Correction of the chemical composition of process water by the ion exchange method.
This method is one of the most modern and economical. It is also called cation exchanger, because the ion exchanger is a cation exchanger resin regenerated with a solution of a strong mineral acid HCl or H2SO. /
When pumping water containing different salts,?’ złoże następuje wymiana kationów — wodór (regeneration of cation with acid) goes into the water, and the cations from the water combine with the functional groups of the exchanger.
The action of cation exchangers is shown in the following reaction:
2 KtH + CaS04->H2SO4 + CaKt2
KtH + NaHCO3 -> CO2 + H2O + NaKt
KtH + NaCl -> HCl + NaKt
where Kt stands for cation exchanger.
There are many types of cation exchangers with different brand names, produced by chemical plants around the world. They are mostly synthetic organic cation exchangers. Their properties depend mainly on the functional groups they have. The most common cation exchangers have sulfo groups and carboxyl groups. Kationity produkcji polskiej — MK-2 i MK-3 — charakteryzują się grupami sulfonowymi.
Water flowing through a cation exchanger with a strongly acidic group loses all its cations, and in their place hydrogen cations are introduced, giving the right acids. Thus, carbonic acid is formed from carbonates, from sulfates - sulfuric acid, from chlorides - hydrochloric acid, from nitrates and nitrites - nitric and nitrous acid.
The carbonic acid formed after the flow of water through the hydrogen cation exchanger immediately decomposes into H2O and CO2. Carbon dioxide which has corrosive properties must be removed by passing water through a suitable degassing device, and possible residues are removed with granular marble. With larger devices and high CO2 content, it is advisable to neutralize the carbon dioxide with lime.
In industrial conditions, water is forced through the ion exchanger column. The water flowing out of the column is directed to the degassing device, and then it is mixed with raw water (water before treatment). Acidified water ratio (after it flows out of the exchanger) for raw water is determined on the basis of the balance of chemical compounds. When calculating the ratio of these parts of water, neutralization of the mineral acids formed on the column should be taken into account, to avoid water corrosivity.