Non Carbonate Hardness

METHODS OF REMOVAL OF HARDNESS OF WATER INTRODUCTION: Water hardness is the traditional measure of the capacity of water to react with soap, hard water requiring considerably more soap to produce lather. Hard water often produces a noticeable deposit of precipitate (e.g. insoluble metals, soaps or salts). It is not caused by a single substance but by a variety of dissolved polyvalent metallic ions, predominantly calcium and magnesium cations, although other cations (e.g. aluminium, barium, iron, manganese, strontium and zinc) also contribute. Water containing calcium carbonate at concentrations below 60 mg/l is generally considered as soft; 60–120 mg/l, moderately hard; 120–180 mg/l, hard; and more than 180 mg/l, very hard (McGowan,

These cations have a tendency to combine with anions (negatively charged ions) in the water to form stable salts. The type of anion found in these salts has therefore been used to distinguish between the two types of hardness-carbonate and non carbonate hardness (Table2).

Table 2 shows that carbonate hardness is caused by Ca2+ and Mg2+ ions combined with anion (CO3 2- or HCO3 - or OH-) to form a salt. In contrast, non-carbonate hardness forms when Ca2+ and Mg2+ combine with anything other than carbonate, bicarbonate, and hydroxide ions.

Carbonate hardness is sometimes called temporary hardness because it can be removed by boiling the water.

The heating of the water can result to decomposition of the salt into metal oxide, carbon dioxide and water and hence removing the hardness.

Non-carbonate hardness cannot be broken down by boiling the water, so it is also known as permanent hardness. In general, it is important to distinguish between the two types of hardness because the removal methods differ significantly. When measuring hardness, it is typically considered the total hardness which is the sum of all hardness compounds in water, expressed as a calcium carbonate equivalent. Total hardness includes both temporary and permanent hardness caused by calcium and magnesium compounds.

REFERENCES:

[1] Research Paper on “Hardness in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality”. Published by World Health Organization in 2011 http://www.who.int/water_sanitation_health/dwq/chemicals/hardness.pdf [Table 1] Research paper on “Removal of Hardness from Groundwater by Synthetic Resin from Waste Plastics” published in “International Journal of Environmental Science and Development, Vol. 2, No. 6, December 2011” http://www.ijesd.org/papers/173-R00021.pdf [2] Research Paper on “Review of hard water treatment

Processes and identification of contaminants” published in “International Journal of Environmental Monitoring and Protection

2014; 1(3): 56-61

Published online August 20, 2014” http://www.openscienceonline.com/journal/ijemp

[Table 2] Research Paper on “Review of hard water treatment

Processes and identification of contaminants” published in “International Journal of Environmental Monitoring and Protection

2014; 1(3): 56-61

Published online August 20, 2014”