الفهرس 
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Abstract
The recommended conditions for acidulating Abu-Tar¬tour phosphate rock with hydrochloric acid are grinding the ore to particle size 800+6Jo Urn, time of acidulation
one hour, acid concentration 7M, 25 °c and using acid, 10 % over the stoichiometri6 amount .
The recommended conditions for acidulating Abu-Tar-
tour nhosphate rock with nitric acid are, using ore of particle size 800-6)0 Urn, time of acidulation )0 minutes a~id concentration 6 M , 25 °c and using acid 10 % over
the stoichiometric .
Th~ dissolution rate per unit geometric surface area
of particles is the same for all particles more finer than 1000 urn for hydrochloric acid and 1600 urn for nitric acid,
whereas it is affected by the particle size for fractions greater than mentioned. The dissolution rate is controlled by diffusion of HCl and HNOJ to the reacting Ca) (P04)2. At the start of interaction the conversion is controlled
by the rate of diffusion of acid through a boundary liquid film surrounding the particles. After the dissolution of Ca3(P04)2 grains at the surface of the particles the conversion become controlled by the rate of diffusion of acid through the pores of an ash layer surrounding embed¬ded Ca)(P04)2 grains inside the particles •
Three distinct dissolution rate ranges can be rep¬resented as follows
ti) Initial constant rate range in which the dissolution rate is given by the equation •
dx/SdQ = K
where K is a constant the value of which is dependent on the temperature of dissolution and on the particle size for fractions coarser than 1000 um for hydro¬chloric acid and 800 um for nitric acid. It is also dependent on the distribution of Ca) (P04)Z at the surface of the particles. It is independent of par¬ticle size for fractions finer than 800 um for HNO) acid and 1600 um for Hcl acid.
(ii)A narrowllrtB.rmediate steep falling rate range in which the dissolution rate is represented by the equ-
ation,
The value of Kz is dependent on the existing excess acid over the stoichiometric requirement.
(iii) A gradually decreasing rate range at that last stage of dissolution which can be represented by the equation ,
Z dx/SdQ = ao + al (I-x) + aZ (I-x)