Minerals Beneficiation - Interaction of British Gum and Dodecylammonium Chloride at Quartz and Hematite Surfaces

The interaction between British gum 9084 and dode-cylammonium chloride (DAC) at quartz and hematite surfaces was established from coadsorption studies and streaming potential measurements. The cationic DAC interacts with the somewhat anionic British gum 9084, leading to the formation and adsorption of a binary complex of DAC-British Gum 9084 at the interface. The parallel ability to depress quartz along with hematite as a result of the interaction between DAC and British gum appears to be the main reason for the ineffective depressant action of starches and starch derivatives in the cationic flotation of iron ores. Amines are not particularly selective collectors for the flotation' of siliceous gangue from iron ores and, therefore, a suitable iron oxide depressant is needed for a satisfactory separation. Various starches and their derivatives have been extensively tested with oxidized iron ores,'-3 and it has been empirically established that British gums and dextrins are preferable. However, for the flotation upgrading of magnetite-taconite concentrates from 8 or 8.5% Si O2 to about 5% Si 02, British gums, which have been used so successfully on oxidized iron ores, have been found to have no effect and oftentimes are actually deleterious.4 In previous articles,5-7, starches were shown by adsorption measurements, flotation tests, and floccula-tion tests to interact with calcium ions in solution, and it was thought that a study on the interaction between starches and dodecylammonium ions would be able to shed some light on the anomalous flotation behavior described above. In fact, starches are known to interact markedly with paraffin-chain-type surface active agents and, thereby, to precipitate the starch or inhibit the iodine-starch reaction.8 From X-ray diffraction studies and viscosity measurements, the formation of a helical complex between mylose and a surface active agent has been postulated.9 The interaction with other types of hydrophilic colloids, such as synthetic polymers and proteins, has also been investigated and is usually explained in terms of van der Waals' force interaction and/or ion-ion interaction. In the present investigation, the interaction of British gum and dode cylammonium chloride on quartz and hematite was studied by adsorption and streaming potential measurements in an attempt to establish the mutual adsorption behavior of British gum and dode-cylammonium chloride on mineral surfaces and to clarify the anomalous depressant activity of British gum in the cationic flotation of iron ores. All the measurements were carried out at a natural pH of near 7 because dodecylammonium chloride gives maximum selectivity of flotation separation at this pH2 and to avoid any third parameter in the system. EXPERIMENTAL MATERIALS AND METHODS Minerals: The quartz and hematite samples used for the adsorption tests were prepared as described in a previous paper,"J except that the specific surfaces of the samples were increased to 5,860 and 16,000 Sq cm per gm, respectively. For the streaming potential measurements, the 48165-mesh fractions screened out of the original samples were etched with hydrochloric acid, washed repeatedly with water, and stored under water in Pyrex bottles. Reagents:DodecyIammonium chloride (DAC) was prepared1 1 by bubbling dry hydrogen chloride gas through a benzene solution of high-purity dodecylamine supplied by Armour and Co. British gum 9084, received from Corn Products Co., was solubilized by first dispersing it in water to produce a 0.05% solution and then homogenizing it in a blender for 5 min. Distilled water was used in the preparation of the samples and the solutions and for all test work. Adsorption Measurements: The procedure for the adsorption density determinations was also the same as that described in the previous paper.1° The residual concentrations of the British gum and the DAC in the supernatant solution were analyzed colorimetrically by the phenol-sulf uric-acid and amine-picrate methods, respectively. The validity of the mine-picrate method for the colorimetric analysis of DAC in the presence of British gum and the analysis of British gum in presence of DAC were checked by establishing calibration curves between optical density and concentration. Streaming Potential Measurements: The cell assembly for the streaming potential measurements was similar to that described by Fuerstenau.' The streaming potential