Abstract
A series of amino acid-based surfactants with a fixed alkyl chain length and with two carboxyl groups separated by a spacer of one, two or three carbon atoms have been synthesized and evaluated as potential collectors for flotation of calcite and fluorite. A monocarboxylate amino acid-based surfactant having the same length of the hydrocarbon tail was also included for comparison in the study. Experiments using a Hallimond flotation tube showed that although the flotation reagents solely differ in terms of spacer, their efficacy in terms of flotation recovery varied very much. Whereas on calcite at pH 10.5 only the monocarboxylate collector gave a high yield, on fluorite at the same pH both the monocarboxylate and the dicarboxylate collectors with one carbon between the carboxyl groups gave good results. On calcite at the natural pH the monocarboxylate collector was most efficient but the dicarboxylate collectors with a two- and a three-carbon spacer also gave a reasonable recovery. On fluorite at the natural pH the dicarboxylate collectors with a two- and a three-carbon spacer were most efficient. The ζ-potential and the flotation recovery of the mineral particles as a function of added collector were assessed and the adsorption was also monitored by diffuse reflectance infra-red spectroscopy. Taken together, the results showed that small changes in the head group region of the collector can radically affect flotation recovery. This type of knowledge is important to understand flotation selectivity in a mixture of similar minerals.
Kurzfassung
Es wurde eine Reihe Aminosäurenbasierter Tenside synthetisiert und als potenzielle Kollektoren für die Flotation von Calcit und Fluorit bewertet. Die Tenside besitzen eine konstante Alkylkettenlänge und zwei Carboxylgruppen, die durch einen Spacer, der ein, zwei oder drei Kohlenstoffatome enthalten kann, getrennt sind. Ein Monocarboxilataminosäuretensid mit der gleichen Kohlenstoffkettenlänge wurde als Vergleichssubstanz in die Untersuchung einbezogen. Experimente in der Hallimond-Flotationsröhre ergaben, dass, obwohl die Flotationsreagenzien sich ausschließlich in Bezug auf die Spacer voneinander unterschieden, deren Wirksamkeit im Hinblick auf die Flotationsanreicherung sich sehr stark veränderte. Während auf Calcit bei pH 10,5 nur der Monocarboxilatsammler eine hohe Ausbeute lieferte, zeigten auf Fluorit beim gleichen pH sowohl der Monocarboxilat- als auch der Dicarboxilatsammler, dessen Spacer zwischen den Carboxylgruppen nur ein Kohlenstoffatom hatte, gute Ergebnisse. Auf Calcit beim natürlichen pH-Wert war der Monocarboxilatkollektor der effizienteste, aber die Dicarboxilatkollektoren mit einem Spacer, der zwei- bzw. drei Kohlenstoffatome enthielt, gab auch eine annehmbare Anreicherung. Dicarboxilatkollektoren mit einem zwei- oder einem drei Kohlenstoffatome enthaltenen Spacer waren auf Fluorit beim natürlichen pH die effizientesten. Das ζ-Potential und die Flotationsanreicherung der Mineralpartikel als Funktion des zugegebenen Kollektors wurden bewertet. Die Adsorption wurde durch diffuse Reflexionsspektroskopie (DRIFTS) überwacht. Zusammengefasst zeigten die Ergebnisse, dass kleine Änderungen in dem Kopfgruppenbereich des Kollektors die Flotationsanreicherung drastisch beeinflussen können. Diese Erkenntnis ist für das Verständnis der Flotationsselektivität in einer Mischung ähnlicher Mineralien von Bedeutung.
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