Water hardness originally refers to the calcium, magnesium ions in the precipitation of the ability of soap. Total hardness of water by means of calcium, magnesium ion concentrations, including carbonate hardness ( i.e. by heating to form carbonate precipitated calcium and magnesium ions, it is also called the temporary hardness ) and non carbonate hardness ( i.e. heating can not settle down part of the calcium and magnesium ions, also known as the permanent hardness ). [1 ]
Said Method
The hardness of the representation is not unified, our country uses more representation method has two kinds: one kind is the measured calcium, magnesium conversion to CaO quality, i.e., per liter of water containing CaO mg number representation, the unit mg L-1; another to meter: 1 Hardness expressed in units of 100000 a water containing 1 copies of CaO (i.e., per liter of water, 1 degrees 10mgCaO ) = 10ppmCaO. The hardness of the said method called the german. [1 ] of water hardness on the said method has many kinds, our country adopts the same representation method and germany. Following the different national representation method.
The German degree ( d ): 1L water containing the equivalent of lOmg CaO, its hardness is 1 German degree ( LD ). This is our country at present the most widely used a water hardness method.
American degree ( mg / L ): 1L water containing the equivalent of LMG CaCO3, its hardness is 1 degrees of the United States of america. Mmol / L: 1L water containing the equivalent of 10Omg CaCO3, called the L mmol / L hardness.
France ( f ): 1L water containing the equivalent of lOmg CaCO3, its hardness is 1 France ( 1F ).
British degree ( E ): 1L water containing the equivalent of 14.28mg CaCO3, its hardness is 1 degrees in the United Kingdom ( Le ). Water hardness general units for mmol / L, also available German degree ( d ) said. The conversion was: 1mmol / L = 2.804 German degree ( d )
Water hardness is divided into carbonate hardness and non carbonate hardness two.
Carbonate hardness
Carbonate hardness: mainly by calcium, magnesium bicarbonate [ Ca ( HCO3 ) 2, Mg ( HCO3 ) 2] the hardness, and small amounts of carbonate hardness. Bicarbonate hardness after heat after decomposition into sediment removed from the water, is also called the temporary hardness.
Non carbonate hardness
Non carbonate hardness: mainly by calcium and magnesium sulfate, chloride and nitrate salts such as the hardness. This kind of hardness can’t use heating decomposition method to remove, so it is also called permanent hardness, such as CaSO4, MgSO4, CaCL2, MgCL2, Ca ( NO3 ) 2, Mg ( NO3 ) 2. Carbonate hardness and non carbonate hardness and called total hardness in water; Ca2 + contents known calcium hardness; Mg2 + in water content known as magnesium hardness; when the total hardness of water is less than total alkalinity, their difference, called negative hardness.
Test steps
Water hardness test disc
In a water sample with pH = 10 ammonia buffer solution and a little chrome black T indicator, solution is red; with EDTA standard solution titration, EDTA and free Ca2 + coordination, with Mg2 + coordination; at the measurement point, EDTA from MgIn – to win the Mg2 +, thus the indicator is freed, the color of the solution changes from red to blue, is the end. When the water is rarely due to Mg2 +, CaIn – MgIn – color sensitivity to many poor, often not keen. In order to improve the end color sensitivity, and can be used in the EDTA standard solution by adding the right amount of Mg2 + ( EDTA calibration before joining, this does not affect the EDTA and the measured ion titration quantitative relationship between ), or in a buffer solution containing a certain amount of Mg – EDTA salt. Total hardness of water by the EDTA standard solution concentration cEDTA and consumption volume V1 ( ML ) to calculate. CaO, unit mg / L. [2 ]
Matters needing attention
Determination of total hardness in ammonia buffer solution pH value regulation. Note that adding masking agent for interfering ions, masking agent before joining in the indicator. Determination of total hardness of time near the terminus should be slow drop shaking. If the water temperature is too low to be measured the water heated to 30 ~ 40º C measurement. [3 ]
Hardness meter
Total hardness microcomputer tester HI96735 market price USD 500
Low range and total hardness reagent HI93735-00 market price USD 100
In the range of total hardness reagent HI93735-01 market price USD 100
High range total hardness reagent HI93735-02 market price USD 100
Measuring range:0-250mg/L(LR), 200-500mg/L(MR), 400-750mg/L(HR)
Resolution:1mg/l(0-100mg/l)
Precision :5mg/L(100-750mg/l)
Measuring way:470nmLBD
How to reduce the water hardness
Automatic water softener is a kind of operation and operation of regeneration process of automatic control of the ion exchange softener, using sodium cation exchange resin for the removal of calcium and magnesium ions in the water, reduce water hardness,add the water softener in The Pretreatment System.so as to achieve the purpose of softening hard water to avoid the carbonate in the pipeline, vessel, boiler fouling. To reach slow down the hardness of the water and protect the membrane.Low investment costs and ensure smooth production.
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