Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / 199 leaves single sided printed, preliminary pages i-vii and numbered pages 1-191. Includes bibliography, list of figures and tables. Digitized using a Hp Scanjet 8250 Scanner to pdf format (OCR). / ENGLISH ABSTRACT: This study provided scientific proof of the precipitation of iron and other metal species in the HAL circuit at the Mineral Separation Plant of Namakwa Sands. Iron and aluminium hydroxides were the most abundant precipitate complexes that formed in the HAL circuit. Sulphates formed bridges with the iron complexes. It was found that precipitation of iron in the HAL circuit was a function of the pH, ferric ion concentration and temperature of the process water. Experimental work provided abundant evidence that the precipitated iron hydroxide and other species adsorb to the surfaces of zircon and rutile mineral particles due to opposite zeta potentials of the mineral particles and iron hydroxide. These adsorbed species altered the electrostatic potential of the mineral surfaces, which reduced the electrostatic separation efficiency of these minerals. It was determined that an improvement of 7% could be expected if the precipitation and attachment of iron could be minimised. Based on the experimental results, conceptual processes were developed and iterative simulations were set up to determine the optimum solution that would maximise the removal of dissolved iron. This solution would ensure clean mineral surfaces free of any adsorbed precipitates. This process circuit was constructed in May to August 2004 at a total capital cost of R4.8m and removed 99.97% of the total dissolved iron prior to caustic addition. Prime zircon recoveries were increased by 3-7%. / AFRIKAANSE OPSOMMING: Hierdie studie het wetenskaplike bewyse gelewer dat yster en ander spesies neerslae vorm in die HAL proses van die Mineraal Skeidings Aanleg van Namakwa Sands. Yster- en aluminium hidroksiede was die vernaamste neerslag komplekse wat gevorm het in die HAL proses. Sulfaat spesies het verbindings gevorm met die yster komplekse. Die neerslag van yster was ‘n funksie van pH, ferric ioon konsentrasie en temperatuur van die proses water. Eksperimentele werk het genoegsame bewyse gelewer dat die yster hidroksied neerslag en ander spesies adsorbeer op die oppervlaktes van sirkoon en rutiel minerale weens teenoorgestelde zeta potensiale van die mineraal partikels en yster hidroksiede. Hierdie geadsorbeerde spesies het die elektrostatiese potentiaal van die mineraal oppervlaktes verander wat sodoende die elektrostatiese skeidingsvermoë van hierdie minerale verminder het. ‘n Verbetering van 7% in elektrostatiese skeiding van sirkoon en rutiel minerale kan verwag word indien die neerslag en adsorbsie van yster minimiseer word. Konseptuele prosesse, gebasseer op die eksperimentele resultate, is ontwikkel. Itteratiewe simulasies is opgestel om die optimum proses te bepaal wat sodoende die maksimum verwydering van die opgeloste yster sou verseker. Hierdie oplossing sou skoon mineraal oppervlaktes, vry van enige geadsorbeerde neerslae, verseker. Hierdie prosesaanleg was opgerig in Mei tot Augustus 2004 teen ‘n kapitaalkoste van R4.8m en dit het 99.97% van die totale opgeloste yster verwyder voordat natrium hidroksied bygevoeg is. Primêre sirkoon opbrengste het sodoende toegeneem met 3-7%.