Dolomite dissolution is not an attractive alternative for meeting Ca²⁺, Mg²⁺ and alkalinity criteria in desalination plants’ post treatment step

Dolomite dissolution is often mentioned as an option for post-treatment of desalinated water for supplying calcium, magnesium and alkalinity to the product water and comply with non-aggres-siveness criteria. This paper uses reliable literature-based dolomite dissolution data to compute and discuss various options for utilizing this process to meet two common sets of desalinated water quality criteria. Alkalinity mass-balance was performed to corroborate literature-data correctness. Discussion shows that CO₂-enhanced dolomite dissolution is impractical due to slow dissolution rates encountered at the relatively high pH values induced by the CO₂ dosage, resulting in low Mg²⁺ concentrations at reasonable retention time. In the H₂ SO₄-enhanced dolomite dissolution the main difficulty arises from the low alkalinity value attained in the water following its blending with raw desalinated water. This, in turn, necessitates very high NaOH dosages to meet required alkalinity and LSI. At relatively low H₂ SO₄ dosages, the post-dilution alkalinity value can be increased, but at the expense of treating the majority of the desalination plant flow, resulting in excessively-high dissolution-reactor volumes. The overall conclusion is that dolomite dissolution is markedly inferior (cost-and quality-wise) to competing Mg²⁺ addition alternatives, including simple dissolution of off-the-shelf chemicals, such as MgSO₄.