Other analytical methods
In order to determine the purity of mineral feed phosphates it is also very important to analyse other elements such as Ca, Fe, Al, Mg, F, Cl, heavy metals,CO2 ,S. Also pH, humidity, density, granulometry, cristallinity, molasses absorption capacity, reactivity and many other physico-chemical parameters must continuously be analysed.
Calcium
The principle of analysing total Ca content is based upon a colorimetric method
Magnesium
The principle of analysing total Mg content is based upon a potentiometric method
But not only the total Mg content is important but certainly the solubility of Mg in buffered solutions as a rumen model.
Mg solubility in Acetate
The Mg solubility in aceate is measured in a buffered solution of constant pH ( 6.5). The concentration of the dissolved Mg is measured.
Mg solubility according to Tovberg Jense
The Mg solubility is measured n at constant pH of 6.5 by automatically titration with HCl. The concentration of the dissolved Mg is measured.
Nitrogen
In case of ammonium containing feed phosphates the nitrogen content is determined by Kjeldahl.
Humidity measurements
In order to determine the free water content in DCP.2H2O it is important that the correct analytical method should be followed. Indeed, drying in an oven at 100 °C (and even at lower temperatures) of dicalciumphosphate dihydrate causes loss of crystal water together with the free water. Principle of the correct method : the phosphate is washed with acetone and after drying on the air the free water content is determined gravimetrically.
The determination of the water content for all the other phosphates ( MCP, MDCP, DICAMAG, MgP ) : drying of the product in an oven during 90 minutes at 80 °C.
In this way it is possible to distinguish dihydrate Dicalciumphosphate from anhydrous dicalcium phosphate.
The presence of CaCO3
Aliphos feed phosphates being produced according to the HCl route Other physicalhave a very high degree of purity (no presence of CaCO3 )with very low levels of undesirable elements (low F and heavy metals content).
The measurement of the CaCO3 is based on a gasometric determination. The developed CO2 volume that escapes when adding an excess of a strong acid to the phosphate is measured. High contents of CaCO3 is an indication for anhydrous Dicalciumphosphate
