High-Performance Fatty Acid Collector for Phosphate Flotation

Transcription

1 CHAPTER 42 High-Performance Fatty Acid Collector for Phosphate Flotation Jue Kou,* Guangyang Xu,* Daniel Tao,* Pablo G. Dopico,t John Hines,t and Dennis Kennedyt ABSTRACT In this paper a number of refilled fatty acid reagents developed by Georgia-Pacific Chemicals LLC were investigated as the collector for flotation of phosphate ore from a phosphate company in Utah, USA. The laboratory flotation tests were carried out at different process parameters such as ph and collector dosage, with both lab deslimed sample and plant deslimed samples in comparison with the collector that was in use at the plant. The results show that collector Gp 0621 was considerably more effective than the collector that was in use at the plant at dosages from 0.35 to 0.65Ib/t. The highest recovery of73.7% was achieved with Gp 0621, which was 5.7% higher than with the plant collector. Higher pulp ph was found to have positive effects on phosphate flotation. INTRODUCTION Phosphate represents a vital nonrenewable mineral resource in the world. It is a commodity which is neither substitutable nor recyclable in agricultural applications. The increased need for world food production assures the long-term growth in world phosphate rock demand. The United States is the world's largest producer and consumer of phosphate rock and the leader in fertilizer production and exports (Stephen, 2003). Phosphate rock requires processing to reduce the content of accessory minerals such as quartz, chert, clay, feldspar, mica, calcite, and dolomite. Typical specifications for phosphate used in phosphoric acid production include (1) P 2 0 S content greater than 30%, (2) CaO/ P 2 0 S ratio smaller than 1.6, and (3) MgO content less than 1 %. If phosphate ore does not meet these criteria, impurities must be removed by some means of beneficiation. There are many beneficiation methods applied in the phosphate processing industry, and flotation is the most Widely used process (Hernainz et al., 2004). It is estimated that more than half of the world's marketable phosphate is upgraded by flotation (Sis and Chander, 2003). Other beneficiation methods such as calcination, acid leaching, and magnetic separation are also being practiced in the industry. However, they have certain limitations and disadvantages when compared to flotation. Sedimentary phosphate upgrading is often accomplished by froth flotation with the or mesh fraction. Flotation takes place in two stages: the primary or rougher flotation using fatty acid collectors to float phosphate, and the cleaner flotation to produce the final concentrate using amine collector to float the entrained silica from the rougher concentrate after deoiling with sulfuric acid. This process is referred to as the Crago double float process, (Zhanget ai., 1997; 'Department of Mining Engineering, University of Kentucky, Lexington, Kentucky, USA tgeorgia-pacific Chemicals LLC, Decatur, Georgia, USA 353

2 354 Reagents and Chemistry Giesekke, 1985) and it is widely practiced in the Florida phosphate industry (El-Shall et al., 2007; 20lO). If the flotation feed contains a high phosphate grade, the second stage may not be used, which is the case in Jordan (Hummadi et al., 1994). The success of the rougher phosphate flotation depends in large part on the performance of the collector added to the ore slurry. Fatty acid collectors, if added with fuel oil, have proven to be effective for rougher phosphate flotation. The phosphate industry is interested in finding new fatty acid collectors that might give increased efficacy. This study was performed to evaluate the performance in rougher phosphate flotation of a number of fatty acid collectors produced by Georgia Pacific Chemicals, LLC (GP) using products obtained from the fractional distillation of tall oil obtained from the pulping of pine trees. EXPERIMENTAl Phosphate Sample The phosphate ore sample used in this study was the plant deslimed flotation feed provided by a phosphate company in Utah, USA. The moisture of the sample was about 18%. Wet sieving was conducted with the sample, and the particle size distribution data for this particular phosphate sample is shown in Figure 1. It can be seen that this sample consisted of 6.85% +600!-lm materials and 35.64% smaller than 150!-lm particles. The dominant size fractions were !-lm and !-lm which accounted for 30.03% and 33.87% of the total sample, respectively. The overall feed grade was 25% P 2 0 S and 21 % A.I. Flotation Experiments Flotation tests were performed using a Denver D-12 lab flotation machine equipped with a 2-liter tank and a 2;;S" diameter impeller. In rougher flotation tests with the plant deslimed phosphate ore, the slurry was first conditioned at 70% solids in a small cell for three minutes after the addition of a certain dosage of collector and diesel. No ph adjustment was made at the request of the phosphate company, and the natural slurry ph was The conditioned slurry was then transferred to a 2-liter flotation cell, and additional tap water was added to dilute the slurry to 35% by weight. Unless otherwise specified, the flotation test lasted 1-2 minutes, and tap water was used in all flotation tests to keep the pulp level constant. A number of GP collectors, including GP 0621, Gp 193G77, GP 193G79, Gp 193G82, Gp 193G83 and 100 o Cumalativeundersize distribution Particle size (JIhl) FIGURE 1. Particle size distribution of plant des limed phosphate sample 1000 Gp 193G84 were evaluated in this study in comparison with the plant collector. The plant dosage was 0.506Ib/ ton for collector and lb/ton for diesel. The same or similar dosages were employed for the GP collectors, and each test was conducted in triplicate to determine the standard deviation of the experimental data. Analysis of P and Acid Insoluble (A.I.) For the purpose of chemical assay, each phosphate sample was ground with a porcelain mortar and pestle. One gram of sample was digested with 50 ml of a digestion acid composed of 40% (vol) HN0 3, 20% (vol) HCl and 40% (vol) H 2 0. Digestion consisted of mixing the digestion acid with solids in a 250 ml volumetric flask, followed by adding de-ionized water to a total volume of 250 ml. The solution was allowed to settle in the volumetric flask for approximately 30 minutes. Then 2.5 ml of supernatant was transferred into 100 ml volumetric flask, and de-ionized water was added to make a solution of 100 ml, which was used for P 2 0 S analysis using an ICP (Inductively Coupled Plasma) instrument (Vista Pro) made by Varian, Inc. (Palo Alto, CA). Acid insolubles (A.I.) were determined from the rest of diluted solution in the 250 ml volumetric flask. The solution was flltered using a frlter paper. The frlter paper with undissolved solids was transferred to a weighed porcelain crucible. The crucible with the frlter paper was placed in a 600 C muffle furnace for 30 minutes. The temperature was then increased to 900 C for one hour. The crucible was cooled to room temperature in a

3 High-Performance Fatty Acid Collector for Phosphate Flotation 355 (jo,-., ::1? t...so ] 1'40 i j JO lj 20 ;- 10 i o.recovery Grade IllFiotationeffteienq IiliYield PlanteonlNlC..P Mll G193f'.82 GP 193f'.84 GP 193f'.83 FIGURE 2. Comparison of flotation resutts (mean values) of plant and GP* Collectors desiccator and then weighed again. The percent insoluble was calculated from the weight difference. RESULTS AND DISCUSSION Effects of Dosage of Different Collectors on Rougher Phosphate Flotation Preliminary testing with several GP showed that GJW 0621 was the best collector for phosphate flotation, and thus it was chosen for flotation evaluation tests at different dosages of 0.35Ib/ton, 0,5061b/ton (plant dosage), and 0.65 lb/ton in comparison with the plant collector at the same three dosages at the natural ph of ph 7.6 in this study. Three other GP collectors, i.e., Gp 193G82, Gp 193G83 andgp 193G84 were evaluated at the plant dosage of0.506ib/ton only. Each test was conducted in triplicate to estimate experimental error. Figure 2 is the comparison of the mean values of the flotation results of all five collectors at Ib/ton, and Figure 3 shows the effects on flotation P 2 0 S recovery and concentrate grade of different collector dosages from 0.35 lb/ton to 0.65 Ib/ton. Figure 4 demonstrates the grade-recovery relationships obtained with the five collectors at different dosages. Figure 2 indicates that the highest P 2 0 S recovery of 54.87% with 31.58% P 2 0 S grade and % yield was achieved with Gp 193G82 at the plant dosage, which was followed by Gp 0621 and the plant collector with recoveries of 51.75% and 49.19%, respectively. Both the recovery and the yield obtained with Gp 193G82 were about 5% higher in comparison with the plant collector. Three GP collectors, including Gp 193G82, Gp 193G84, and Gp 0621 consistently produced a concentrate P 205 grade above 30%. The fact that GIW 193G82 and GJW 0621 generated higher concentrate grade and recovery and greater flotation efficiency indicates that both Gp collectors had greater collecting abiliry for phosphate and better selectivity between phosphate and quartz. Additionally, both Gp 0621 and Gp 193G82 produced more stable foam than other collectors, and no frother was needed in the flotation tests. It is well known that the flotation separation performance is strongly dependent on the collector dosage. A series of flotation tests were conducted at different collector dosages to investigate the dosage effect and the results are shown in Figure 3. It is quite obvious that the flotation recovery obtained with the plant collector and Gp 0621 increased significantly with increasing the dosage from 0.35 lb/ton to 0.65 lb/ton, and Gp 0621 achieved higher recovery than the plant reagent at all three dosages. At a dosage ofo.5061b/ton, Gp 0621 produced 2.5% higher recovery than the plant collector. The difference in recovery was even greater at the highest collector dosage. At a dosage ofo.65ib/ton, Gp 0621 achieved the highest recovery of73.70%, which

4 356 Reagents and Chemistry Plant Collector Recovery --G1' 0621 Recovery GI' 1'3G82 --Plant Collecror Grade ";' 3S -e-gi' 0621 Grade '-' ";' to '-' O,l O,l "0 40 (If t./ GI' 19JG8J &!coveryat plant dosage Dosage (lb/ton) FIGURE 3. Comparison of flotation results (mean values) of plant collector and Gp Collectors at different dosages was 5.7% higher than that obtained with the plant collector. The recoveries produced with Gp 193G82, Gp 193G83 and Gp 193G84 at a dosage 0.506lb/ton are also shown in the plot. Gp 193G82 had a similar performance to Gp 0621 whereas Gp 193G83 and Gp 193G84 produced inferior results to Gp Figure 4 shows the relationship between P 2 0 S recovery and grade obtained with the Gp collectors and plant collector. The curves or points closer to the upper right corner represent more efficient separation. Regardless of the collector, the highest recoveries are generally obtained at the lower grades, and conversely, in order to get the highest grades, lower recoveries must be accepted. The data in Figure 4 indicate that the recovery decreased sharply with increase in concentrate grade above 30% for the plant collector and 30.5% for Gp In comparison, Gp 0621 always produced higher recovery at a given grade than the plant collector, which further confirms that Gp 0621 is more selective than the plant collector in floating phosphate. Gp@ 193G82 and Gp 193G84 also produced better separation than the plant collector since their data points are above the separation curve for the plant collector. Only GP@ 193G83 showed inferior performance than the plant collector, which is consistent with Figure 2 that shows Gp 193G83 resulted in the lowest recovery and grade. The standard deviations for the triplicate tests were mostly <2% for P 2 0 S recovery and < 1 % for the P 2 0 S grade. Considering the factors such as fluctuations in feed P 2 0 S grade, system errors associated with ICP analysis, etc., the test results are considered sufficiently accurate and reliable. The flotation feed received from the plant contained a small amount of -200 mesh particles or slimes, as shown in the size distribution curve in Figure 1. To evaluate the effect of slimes on flotation performance, the as-received feed sample was deslimed in the lab by wet screening at 200 mesh. The slime-free phosphate sample was then floated using three GP collectors, i.e., Gp 0621, Gp 193G77, Gp 193G79, and the plant collector in triplicate flotation tests under the conditions of ph 7.6, 0.506Ib/ton collector with 0.639Ib/ton diesel. Figure 5 and Table 1 show the mean values of flotation results with these four collectors. The data show that significantly higher flotation recovery was achieved with the lab deslimed sample, suggesting that the slime had major effects on flotation efficiency. For example, in Table 1, the data show that a 73.76% recovery at 27.52% grade was achieved with O.5lb/ton Gp@ 0621 in the lab deslimed sample. In contrast, when using the sample which was not deslimed,

5 High-Performance Fatty Acid Collector for Phosphate Flotation ';' 50 t, 40 --Plant Collector c:> <.i <II GP GP 193G83 10 GP 193G Grade (Of.) the same collector only achieved a recovery of % at 0.5 lb/ton, and it required a higher collector dosage of 0.65 lb/ton in order to achieve a recovery of73.70% (see Figure 4). Comparing the collectors tested using the lab deslimed sample, Gp 0621 achieved the highest recovery of 73.76% with 27.52% P 2 0 S grade, and the plant collector resulted in 68.39% recovery with a concentrate grade of about 26.65%. In other words, Gp 0621 produced 5.37% higher recovery at 0.87% higher grade. Obviously, Gp 0621 was more effective than the plant collector for the deslimed sample. The other GP collectors were less effective than the plant collector. It should also be noted that Gp 0621 produced more stable flotation performance than the plant collector, since the standard deviation in recovery was 0.92% for the Gp collector and 2% for the plant collector. FIGURE 4, Relationship between P 2 0 S recovery and grade with GP and plant collectors,-, e..., 8& '" 60 I <II 1:1 40 t1 i "f.20 6 _Recovery _Grade _ Flotation effidency PlantCellector Gf'(i) 193G77 Gf'(i) 0621 Gf'(i) 193G79 FIGURE 5. Flotation performance with lab deslimed sample using plant and different GP collectors TABLE 1. Flotation test results with lab deslimed phosphate sample using different collectors Grade Acid insolubles Yield Recovery Collector (%) (%) (%) (%) Plant Collector GP GP 193G GP 193G Flotation efficiency (%)

6 358 Reagents and Chemistry CONCLUSIONS The following major conclusions can be derived from the data shown above: 1. Gp 0621 was more effective than the plant collector in the flotation of plant deslimed phosphate at three different dosages. Recoveries of73.7% and 51.75% were achieved with Gp 0621 at a dosage of 0.65 Ib/ton and 0.s06Ib/ton (plant dosage), respectively, which were significantly higher than those obtained with the plant collector at the same dosage. An increase of more than 5% in flotation recovery can be expected if Gp 0621 is used as collector at 0.65 Ib/ton. 2. Among three Gp collectors of Gp 193G82, Gp 193G83 and Gp 193G84, Gp 193G82 produced a recovery of 54.87%, which was 5.68% higher than that generated with the plant collector at the plant dosage ofo.506ib/ton, respectively. Other GP collectors had lower recoveries at the dosage tested. Gp 0621 and Gp 193G82 collectors also produced more stable foam, and no frother was needed for the flotation. Gp 193G82 is likely the best collector, although additional tests under different conditions may be needed to verify this conclusion. 3. More complete desliming of phosphate flotation feed considerably increased flotation recovery, which allowed the use oflower collector dosages to achieve the same recovery. A 73.7% recovery was achieved with 0.5 lb/ton ofgp 0621 with lab deslimed samples, and a higher dosage of 0.65 Ib/ ton of the same collector was required to achieve the same recovery when using samples that were not deslimed in the laboratory. 4. As was the case when using the plant deslimed ore, when using the cleaner lab deslirned ore Gp 0621 showed better recovery and grade than the plant control. An increase of more than 5% in flotation recovery and about 1.5% in P 2 0 S grade was achieved when Gp 0621 was used at the same dosage as the plant collector. REFERENCES El-Shall, H., Miller, J.D., Somasundaran, P., Stana, R., Wang, G., Effect of particle characteristics on fatty acid flotation of Florida phosphate rock. Final Report to Florida Institute of Phosphate Research, Publication No El-Shall, H., Zhang, P., Abdel Khalek, N., Somasundaran, P., Phosphate flotation practice. In Froth Flotation, A Century ofinnovation, Ed. By M.e. Fuerstenau, G.Jameson, and R.-H. Yoon, SME, pp Giesekke, E.W., Florida phosphate rock. SME Mineral Processing Handbook, Section 21, pp Hernainz, F., Calero, M., Blazquez, G., Flotation oflow-grade phosphate ore. Advanced Powder Technology. 15, n4, pp Hummadi, N., Oweis, 1., Mubaideeu, M., Flexibility in rock phosphate flowsheets to meet the specific requirements of individual plants. In Proceedings of thelf A Technical Conference, Amman, Jordan, October 2-6. Sis, H. and Chander, S., Reagents used in the flotation of phosphate ores: a critical review. Minerals Engineering. 16, pp Stephen M. Jasinski, Phosphate rock. U.S. Geological Survey, Mineral Commodity Summaries. Zhang, P., Yu, Y., Bogan, M., Challenging the "Crago" double floate process ii. Amine-type-fatty acid flotation of silicious phosphates. Minerals Engineering. 10, pp