Minerals Beneficiation - An Infrared Study of the Flotation of Hematite with Oleic Acid and Sodium Oleate

Infrared spec troscopy was used to study the adsorption of oleate collector on three varieties of hematite. Each of the minerals was found to react with either oleic acid or a solution of sodium oleate to form a mineral cation-collector anion chemisorbed layer at the solid-liquid interface. The chemisorption reaction displaced surface hydroxyls and was found to be pH dependent. The infrared band characteristic of the antisymmetrical C = 0 structural group of chemisorbed oleate appears between 1520 and 1540 cm-'. Evidence is presented which shows that molecular filming of the mineral surfaces with un-dissociated oleic acid precedes chemisorption. Infrared absorbance is correlated with the flotation behavior of the mineral. Adsorption processes are usually classified into two types which are distinguished and character- ized by the nature of the bond formed between the adsorbate and adsorbent. The process in which molecules chemically bond to solid surfaces is termed activated adsorption or chemisorption. If only weak van der Waals forces bind the molecules to the surface then the process is termed physical adsorption. Chemisorption is of primary interest in flotation systems since selectivity may be obtained if a single mineral is rendered air-avid by a specific collector mineral adsorption reaction. In previous studies infrared spectroscopy was used to define the mechanisms involved in the adsorption of oleic acid and sodium oleate on fluorite, barite, and calcite. Infrared techniques were particularly useful since adsorbed monolayers were identified in situ. Further, the infrared method permitted identification of reaction products in the solid, liquid, and vapor phases of the systems. The chemisorption reactions displaced F- from fluorite, SO4 from barite, and CO3 from calcite. This investigation was pursued in an effort to characterize and interpret the adsorption processes for synthetic hematite, compact red hematite, and specular hematite (crystalline hematite). Adsorption tests were performed using either oleic acid or