Novel surfactants to enhance collectors for the direct flotation of apatite

As the world’s population continues to grow, so does the demand for fertilizers to reduce the risk of food insecurities. Roughly 50 percent of global food production is due to fertilizers. The mining and processing of phosphate ore (apatite) continues to be the dominant pathway of yielding phosphorus-based fertilizers (diammonium phosphate). However, the phosphate (P2O5 ) concentration in the raw ore does not possess the grade that is economical to process at fertilizer chemical plants. Therefore, beneficiation must occur, but it faces challenges. These challenges include obtaining high recoveries of industry-specified-quality mineral concentrates while using feedstocks of ever-declining quality. A novel alkylpolyglucoside-type (Mod APG, Cola Float 1500) surfactant was developed, and its enhancement of the flotation properties of a standard fatty acid collector was investigated with the goal of achieving an improved grade/recovery of apatite. Introduction A typical apatite concentrate, post rougher and cleaner flotation, will contain more than 28 percent P2O5, less than 10 percent acid insolubles (quartz), and other plant and product specific specifications, such as MgO, Fe2O3 and Al2O3. However, the rougher circuit generally targets more than 22 percent P2O5 to maintain the throughput and economics for the beneficiation plant. The first-stage flotation (rougher) of apatite from gangue minerals historically uses a saponified fatty acid collector to ligate with the sparingly soluble calcium on the surface of the phosphate particles. However, ore quality has greatly decreased over the years for the apatite feedstock, which has made it necessary to move to a more sophisticated formulated collector package to achieve optimal grade and recovery. Formulators will combine surfactants to help manipulate the froth properties, wet the mineral surface, impact the coordination properties with minerals to improve selectivity, or even manipulate contaminants in the process water. Materials and methods All of the surfactants were produced by Colonial Chemical, and their surfactancy properties were measured and reported as surface tension, critical micelle concentration (CMC) and chelation value (Table 1). These surfactants were evaluated individually as well as in formulation with saponified fatty acids toward the impact of foam height, bubble count and rate of foam coalescence. These formulations were also evaluated for potential enhancement in the recovery of and selectivity for apatite. Results and discussion In colloidal and surface chemistry, the CMC is a measurement of the surfactant concentration required for micelle generation (Fig. 1). At a time of 309 s after aeration was complete, it can be concluded that the surfactants with lower CMCs generated a more stable foam that also had a higher bubble count. The properties of foam can be related to surfactant efficiency at reducing the water surface tension. Generally, a reduction in surface tension should yield a more stable bubble. These enhancements will also possess coordination properties that can have an impact on the mechanism expected from a Na-fatty acid/apatite flotation system. That is how they coordinate, as well as what happens when they do. Considering the point of coordination for apatite is the calcium, the chelation value was analyzed for calcium. According to the chelation value presented in Table 1, it can be concluded that the Mod APG can tolerate a much higher concentration of calcium, while the APG-phosphate precipitated nearly immediately with the lowest addition of calcium. However, the surfactants’ role is not as simple as froth manipulation or coordination properties. It must generate the conditions required for one mineral to selectively separate from the others and join this froth as it floats out of the cell. Rougher flotation feed was collected and found to contain 7.19 percent P2O5 and 77.13 percent acid insolubles (insol). This plant generally focuses the rougher cells on the highest P2O5 recovery possible while achieving a minimum grade of 25 percent P2O5 and less than 30 percent insol. Using 0.5 kg/t of saponified fatty acid (Na-fatty acid), a recovery of 85 percent was achieved (Fig. 2). Increasing the dosage did not further improve the P2O5 recovery. The higher dosage yielded more insol flotation and pushed the P2O5 concentration to below the 25 percent target. Fig. 1 Impact of surfactants on foam properties after 309 s. The Na-sulfosuccinamate yielded an overwhelming froth that surprisingly contained minimal amount of any mineral, gangue or apatite. By enhancing NA-fatty acid with APG phosphate, the recovery was increased by 5 percent points (90 percent recovery) at a dosage of 0.5 kg/t, relative to Na-fatty acid without enhancement. However, a higher dosage pulled too much insol and made the grade fall below the target of 25 percent P2O5. The enhancement that yielded the best performance was with Mod APG. This enhancement provided a recovery of 93 percent, which was 8 percent points higher than Na-fatty acid without an enhancement. It is not mandatory for the primary rougher flotation to achieve the polished contaminant concentration (Al2O3, Fe2O3, MgO). It is usually managed in the cleaner cells. In theory, if the process is set to pull harder, more of these contaminants should also be coming with the concentrate. In this case, enhancing with Mod APG did not negatively impact the (Fe + Al)/P ratio (Fig. 3). In fact, a ratio of 0.074 was achieved, compared to the final cleaner target of less than 0.087. Fig. 2 Balance of grade versus recovery. Conclusion As the feed grade of raw apatite ore continues to decline, it is becoming more difficult to obtain the volume of concentrated P2O5 required for the world’s fertilizer demand. The chemical plant can attempt to process more volume to support this demand, but another strategy would be to improve the efficiency at which the beneficiation plant is currently running. This can be done by tailor-making surfactants to enhance the current fatty acid collector system. Enhancements can be seen in the way of froth properties, coordination or ligation characteristics of the collector package, or even surface modification of the mineral itself. Colonial developed such an enhancement, considering all these properties. Fig. 3 Microscopic view of flotation feed, concentrate and tails obtainedwith NA-fatty acid enhanced with Mod APG. Mod APG (Cola Float 1500) yielded the lowest CMC and the highest chelation value of the surfactants evaluated. By enhancing saponified fatty acid with Mod APG, 93 percent recovery was obtained for a rougher concentrate that is 25.7 percent P2O5 and 24 percent insol and has a (Fe2O3 + Al2O3)/P2O5 ratio of 0.074. References A list of all references is available in the full paper.

Novel surfactants to enhance collectors for the direct flotation of apatite

Authored by: Lucas R. Moore, Jordan D. Taylor and Jonathan Hardy

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