Abstract
This study investigated the removal of phosphorus from waste phosphogypsum by using citric acid as
a leaching
reagent, evaluated the potential environmental effect of the final product produced and provide
recommenda- tions for the application of developed products. A dissolution process was applied and
three variables were studies namely, concentration, stirring speed and temperature. The results
showed that Phosphorus can suc- cessfully be removed from waste phosphogypsum and the optimum
leaching conditions were at the con- centration of 0.5 M and temperature of 40 °C, with no effect
observed on varying the stirring speed. Shrinking core model (SCM) was used to determine the best
fit for the experimental data. For the pore diffusion model (KD), all correlation coefficients yielded
were above 0.9, illustrating a positively linear correlation of KD and leaching behavior for
phosphorus. Pore diffusion proved to be the effective rate controlling mechanism for the removal of
phosphorus from phosphogypsum. The analysis of moments of particle size distribution (PSD) also
showed a reduction in particle size, indicating the dissolution of the solid particles. The
application of Toxic Leaching Characteristic Procedure (TLCP) showed low concentrations on the
effluent, indicating that the de- veloped product will not contaminate the environment through
leaching. The obtained leachate concentrations were within the South African effluent discharge
standards. The results also showed that dissolution had a significant contribution on the moments of
particle size distribution, in terms of the volume, surface area and particles number. In respect
to unconfined compressive strength the products developed can be used for load
bearing and as backfill material.