Rate of Solution of Solid Particles in Agitated Liquids

Abstract

Hixson and Baum have proposed generalized dimensionless equations for the rate of solution of solid particles in agitated liquids. The authors developed an improved equation and conducted additional experiments on the rates of solution of zinc and magnesium metals in dilute hydrochloric acid containing potassium nitrate. Experiments were also made on the rate of solution of benzoic acid in NaOH solutions and of sugar in water. The newly developed equation is as follows: (KD/Df)=α′(D²nρₗ/µ)ᵖ(µ/ρₗFf)q(δ³g/ν²)r(ρₛ-ρₗ/ρₗ)ᵗ The constant α′ and exponents p, q and s are presented in this paper. The authors arrived at the following conclusions: (1) At a definite critical Reynolds number, Rf (or agitator speed, Nf), solid particles are fluidized in an agitated liquid. (2) At this critical Reynolds number (or agitator speed), the rate of increase in solution velocity is abruptly decreased with further increase in agitator speed. (3) In the fluidized state where N>Nf, an increase in density difference between the solid and liquid phases combined with the effect of agitation velocity greatly reduces the diffusional resistance. (4) In the range of Reynolds numbers less than Rf, or agitator speed less than Nf, the apparent rate of solution of solid particles increases with the 1.0 to 1.4 power of Rₑ depending upon the conditions of agitation. This experimental effect may reach a value of even 2.9 for small particles. (5) From these experiments it is expected that the effect of agitation in liquid-liquid systems is mainly to increase the reaction surface area, and that the effect of agitation in diminishing diffusion resistance is rather small. The effect of agitation in solid-liquid systems in the range of fluidization is mainly to diminish diffusional resistance.