Temporary hardness

Temporary hardness of water is a condition where the water contains dissolved bicarbonate minerals that can precipitate out as calcium carbonate (CaCO3) or magnesium carbonate (MgCO3) when the water is heated. This type of hardness is distinguished from permanent hardness, which is caused by the presence of sulfates and chlorides of calcium and magnesium that cannot be removed by boiling. Temporary hardness is significant in various contexts, including water supply, water treatment, and brewing.

Causes

Temporary hardness is primarily caused by the dissolution of calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2) in water. These compounds are soluble in water and can easily be precipitated out as their carbonate forms when the water is heated or when its pH is altered. The source of these bicarbonates is usually the interaction of water with limestone (calcium carbonate) and dolomite (calcium magnesium carbonate), through which the water acquires its hardness.

Effects

The effects of temporary hardness include scaling inside pipes, boilers, and kettles due to the precipitation of calcium and magnesium carbonates. This scaling can reduce the efficiency of heating elements and increase energy consumption. In the textile industry, temporary hardness can affect the dyeing process, leading to uneven dye uptake and color. In brewing, the presence of certain levels of temporary hardness is desirable as it can enhance the flavor of the beer, but excessive hardness can lead to scaling in brewing equipment.

Measurement and Treatment

The level of temporary hardness in water is typically measured in degrees of hardness, often expressed in parts per million (ppm) of calcium carbonate. Treatment methods for reducing temporary hardness include boiling the water, which precipitates out the bicarbonates as carbonates that can be removed by filtration. Another method is the use of ion exchange resins, which can remove calcium and magnesium ions from the water, thereby reducing its hardness.

Environmental and Health Considerations

While temporary hardness does not pose a direct health risk, the scale buildup can lead to inefficiencies in water heating systems, potentially increasing energy consumption and costs. From an environmental perspective, the treatment and removal of hardness from water, particularly in large-scale water treatment facilities, can involve the use of chemicals and generate waste products that need to be managed responsibly.

See Also

• Water softening
• Hard water
• Lime softening
• Ion exchange