Otavite-calcite solid solutions have been synthesized to investigate the factors which control the patterns of compositional zoning. The equilibrium partitioning of otavite between the aqueous and the solid phase can be described by means of a functionXCdCO₃(X_Cd,aq)_eq, which relates the solid mole fraction and the aqueous activity fraction of Cd. According to this function, there is a strong preferential partitioning of Cd towards the solid. A set of experiments starting with parent solutions with different Cd²⁺/Ca²⁺ratios was carried out. In these experiments nucleation takes place at high supersaturations and the Cd²⁺and Ca²⁺ions tend to be laid down in a ratio which deviates from the equilibrium distribution. Experimental nucleation data can be fitted to a curveXCdCO₃(X_Cd,aq)_efof the same functionality as that for equilibrium.After nucleation, supersaturation decreases as the crystals grow. During this process, substituting ions are not incorporated into the solid in the same stoichiometric proportion as in the aqueous solution. Therefore, crystal and fluid compositions tend to vary as growth proceeds and this evolution is registered as a compositional zoning. The curvesXCdCO₃(X_Cd,aq)_eqandXCdCO₃(X_Cd,aq)_efconfine the reaction path corresponding to the growth process. Here, these curves are used to account for the observed zoning patterns.

This work evaluates the use of a synthetic NaP1 zeolite obtained from a hazardous Al-containing waste for the removal of ammonium (NH₄⁺) from aqueous solutions by batch experiments. Experimental parameters, such as pH (6–8), contact time (1–360 min), adsorbent dose (1–15 g/L), and initial NH₄⁺ concentration (10–1500 mg/L), were evaluated. Adsorption kinetic models and equilibrium isotherms were determined by using nonlinear regression. The kinetic was studied by applying both the pseudo-first-order and pseudo-second-order models. The equilibrium isotherms were analyzed according to two-parameter equations (Freundlich, Langmuir, and Temkin) and three-parameter equations (Redlich–Peterson, Sips, and Toth). The results showed that the NH₄⁺ uptake on NaP1 was fast (15 min) leading to a high experimental sorption capacity (37.9 mg/g). The NH₄⁺ removal on NaP1 was a favorable process that followed the pseudo-first-order kinetic model. The NH₄⁺ adsorption was better described by the Sips (54.2 mg/g) and Toth (58.5 mg/g) models. NaP1 zeolite from Al-waste showed good NH₄⁺ sorption properties, becoming a potential adsorbent to be used in the treatment of contaminated aqueous effluents. Thus, a synergic effect on the environmental protection can be achieved: the end of waste condition of a hazardous waste and the water decontamination.