Inclusion of isomorphous impurities during crystallization from solutions

Growth and characterization of KDP crystals with potassium carbonate as additive

“…The capture of an impurity in a crystal during its growth from a solution is the combined effect of various factors: the solubility of the host and the impurity phase, character of the mother phase, interaction between the host and the impurity molecules, relative size of impurity and host ions, similarity in the crystallographic structure of the two phases, relative size of the impurity and the host ions and other crystallization conditions [9]. The impurity effect depends on the impurity concentration and supersaturation, temperature and the pH of the solution.…”

Chemical, Physicochemical and Crystal-Chemical Aspects of Crystallization from Aqueous Solutions as a Method of Purification

“…Spectacular examples of a huge effect of this factor on D 2/1 are given by (Urusov, 1977) where during the crystallization from the melt in systems NaBr -AgBr, NaCl -AgCl, and NaCl -CuCl, co-crystallization does not take place, although the relative differences of interionic distances of co-crystallizing isomorphous salts are very low or close to zero. The difference in the effective ionic charges of Ag(Cu) and Na in these systems was believed to be responsible for the extremely low miscibility of these systems (Kirkova et al, 1996).…”

“…As temperature increases, the solubilities of the macro and microcomponent (m 01 , m 02 ), the mean activity coefficients in their binary saturated solutions ( m01 ,  m02 ), the mean activity coefficients in the ternary solution being in equilibrium with their mixed crystal ( m1 ,  m2 ) (temperature affects dehydration of ions, processes of hydrolysis or complex formation in solution (Kirkova et al, 1996), as well as activity coefficients of both in their solid solution (f 1 , f 2 ) (temperature influences enthalpy of mixing in the solid phase) change in different directions in various crystallization systems. Therefore, both the increase and drop of co-crystallization coefficient may be observed or sometimes the maintenance of its constant value (in the case of compensation of the all mentioned changes).…”

“…However, a kind of dependence of D 2/1 coefficients on electronegativity has not been univocally defined and the kind of function () is very important to decide if unilateral isomorphism occurs, in spite of a buffering action of surrounding hydrate mantle (Kirkova et al, 1996). (Smolik, 2004) To evaluate if unilateral isomorphism occurs during low temperature crystallization from aqueous solutions (according to the rule known for a long time in geology [Urusov, 1970] that lithophilic elements are substituted in the solid phase by chalcophilic and siderophilic elements and not to the contrary) several criteria may be applied (Smolik, 2004).…”

“…Substituting concentrations of microcomponent (2) and macrocomponent (1) in equation (3) with their activities (a 1S , a 2s , a 1r , a 2r ) it is possible to obtain an expression for thermodynamic co-crystallization coefficient D o 2/1 . (Kirkova et al, 1996;Ratner, 1933 (2) and (1) respectively during the transition from the liquid phase (r) into the solid phase (s). Two cases should be distinguished here: 1) substance (2) is not isomorphous with substance (1), i.e., it crystallizes in different crystal systems (different space groups); 2) substance (2) is isomorphous with substance (1).…”