The temperature and ionic strength dependence of the solubility product constant of ferrous phosphonate

[摘要] The formation of ferrous phosphonate precipitate and its dissolution were monitored in a batch experiment for a range of temperatures and ionic strengths. The precipitate was found to be Fe$sb{2.5}$HNTMP, where NTMP is a phosphonate compound. Using a complexation and speciation model, concentrations of free iron and phosphonate were calculated, from which the solubility product constant was derived for each temperature and ionic strength. The temperature (K) and ionic strength (M) dependence of the negative logarithm of the ferrous phosphonate solubility product constant $(pKsb{m sp})$ was thus determined:$$pKsb{m sp} = 39.54 - 6.14sqrt{IS}+2.18IS - 1315/T.$$Simulated calculations using actual field data to compare iron and calcium phosphonates predicted ferrous salts to form in all instances and calcium salts to form occasionally. Further, a relationship was established whereby the concentration of free iron in a calcium-iron-phosphonate system can be predicted.

[发布机构] Rice University

[效力级别] chemistry