Studies on nucleation and crystal growth kinetics of ferrous oxalate

An improved apparatus is used for nucleation measurements according to Nielsen's method. A new method is proposed to calculate the dilution ratio N of the reaction solution during nucleation rate determination. With the rule, when the initial apparent supersaturation ratio S'=f(N) in the dilution tank is controlled from 1.3 to 3.0, crystal nucleus dissolving and secondary nucleation can be avoided satisfactorily. Experiments are realized by varying the supersaturation ratio from 15.6 to 93.3 and temperature from 15 degrees C to 50 degrees C. Ferrous oxalate is precipitated by mixing equal volumes of ferrous sulfate and oxalic acid solution. The experimental results showed that the nucleation rate of ferrous oxalate in the supersaturation range above is characterized by the primary homogeneous mechanism and can be expressed by the equation R-N = A(N)exp(-E-a/RT)exp[-B/(ln S)(2)], where A(N) = 3.9x 10(13) m(-3) s(-1), E-a = 33.9 kJ mol(-1), and B =13.7. The crystal growth rate can be expressed by equation G(t)=k(g)exp(-E'(a)/RT) (c-c(eq))(g), where k(g) = 3.6 x 10(13) m/s, E'(a)= 58.0 kJ mol(-1), and g = 2.4.