Disodium Hydrogen Phosphate (DSP)

About This Product

Disodium hydrogen phosphate, DSP, has the formula Na2HPO4 and CAS number 7558-79-4, supplied anhydrous or hydrated as a white crystalline powder. It results from neutralising two of the three protons on phosphoric acid, and dissolves to a mildly alkaline solution around pH 9. Paired with the acidic monosodium salt it forms the standard phosphate buffer, and the ratio between the two sets the pH anywhere across a broad band. That buffering is used industrially wherever a process would otherwise drift: in electroplating baths, in textile dyeing where shade depends on pH, and in fermentation. In boiler water treatment it serves a different purpose. Calcium in feedwater otherwise deposits as calcium carbonate or sulphate scale, which is hard, adherent and insulating. Dosing phosphate precipitates the calcium instead as hydroxyapatite, a soft sludge that stays mobile and can be blown down rather than baking onto the tubes. It is also a detergent builder, sequestering hardness ions so surfactant is not wasted, and it finds use as a fireproofing agent for timber and textiles. It is used in boiler water treatment, detergents and cleaners, electroplating and metal finishing, textile processing, fireproofing and as a buffer. Bio Green Chem supplies DSP to specification on assay, pH, loss on drying, water-insoluble matter, chlorides, fluoride and heavy metals.