Influence of polyphosphonates on the precipitation of strontium sulfate (Celestite) from aqueous solutions

The precipitation of strontium sulfate from aqueous solutions in the presence of polyphosphonates at 0.7 mol l−1 sodium chloride and 25°C has been studied. Over a range of relative super-saturation (2.0 − 6.2) the process appears to follow a surface controlled precipitation mechanism which is markedly inhibited by the presence of additives. The presence of phosphonates even at relatively low concentrations (2.5 − 20 × 10−6 mol l−1) were retarding the rate of precipitation. The retardation effect of these additives has been attributed to the blocking of active sites by adsorption of additives molecules at the crystal precipitation surfaces. The action of additives can be interpreted in terms of a Langmuir-type adsorption isotherm.