磷矿选矿文献-外文文献部分2012-the beneficiation of ultrafine phosphate

1、Minerals Engineering 2728 (2012) 5259The beneciation of ultrane phosphateA.J. Teague , M.C. LollbackLegend International Holdings Inc., Level 8, 580 St. Kilda Road, Melbourne, Vic. 3004, Australiaa r t i c l e i n f oa b s t r a c tArticle history:Received 20 October 2011Accepted 12 December 2011Ava

2、ilable online 29 December 2011This paper discusses a novel method of beneciation of ultrane phosphate which allows the recovery of phosphate particles that are less than 20 lm in size and have long been considered in the industry to be unrecoverable. It has been standard practice over many years in

3、the phosphate industry to separate and discard the ultrane particles, due to unacceptable processing difculties such as excessively high viscos- ity and/or poor otation recovery. In contrast with the established methods of beneciation of phosphate where classication by hydrocyclone is mainly used to

4、 remove ultranes as tailings, the method described in this paper allows a high proportion of ultranes to be recovered via otation without prior separation.A number of variables and their effect on the otation recovery of ultrane phosphate are investigated including the pulp density and water quality

5、 during conditioning and otation, type of otation machine and reagents used to depress Fe2O3 and Al2O3. Some excellent results were achieved using samples con-Keywords:Industrial minerals Fine particle processing Flotation machines Flotation depressants20 lm particles, including for example 91.2% P2

6、O5 recovery to a concentrate gradetaining up to 75 wt%of 34.7% P2O5 from a low feed grade of 6.46% P2O5 and 92.4% P2O5 recovery to a concentrate grade of 30.2% P2O5 from 10.6% P2O5 feed. Guar gum was found to be the most effective depressant for Fe2O3, whilst the Al2O3 was determined to be hydrophil

7、ic, resulting in low amounts being recovered to the con- centrate, regardless of whether a depressant was used or not. The results of this work led to the devel- opment of the method described herein which is designed to recover phosphate from ores containing particles up to 80 wt% passing 20 lm, by

8、 otation using a Jameson cell.Crown Copyright 2011 Published by Elsevier Ltd. All rights reserved.1. Introductionphate (Teague and Lollback, 2010). After grinding, the proportion of ultranes can increase to up to 80 wt% of the total feed mass, containing up to 75 wt% of the phosphate. At the beginni

9、ng of the development of Legends beneciation process, it became clear that if standard practice was followed by desliming and discarding the ultranes, the project would be potentially uneconomical due to the removal of a large portion of the phosphate values. Hence the major aim of this work was to

10、develop a process that could suc- cessfully concentrate ore from either of these two major phosphate deposits without discarding any ultranes.Bench scale otation tests were initially carried out in a conven- tional Denver cell to conrm the poor oatability of the ultrane phosphate and to investigate

11、the effect of pulp density and water quality during conditioning and otation, on phosphate recovery. Some bench scale comparison tests between Denver cells and Jame- son cells were carried out, which effectively nalised the design of Legends beneciation process. Lastly, the entire beneciation pro- c

12、ess was set-up at laboratory pilot scale to test diamond drill core and RC chip samples, to enable Legend to calculate a reserve for the Paradise Southanda pending reserveforthe DTreeoredeposits. These tests conrmed the novel process was successful using sam- ples with highly variable phosphate feed

13、 grades and mineralogy and also established guar gum as the best depressant for Fe2O3.Phosphate beneciation operations around the world which use otation as the principal mechanism to concentrate the phosphate bearing minerals, typically discard the ultrane phosphate bear- ing particles, where for t

14、his study ultrane is dened as particles being smaller than 20 lm. It is standard practice in the phosphate industry to separate the ultranes by scrubbing and hydrocyclon- ing before the remainder of the raw feed is transferred to the ota- tion plant for concentration (Kogel et al., 2006). Phosphate

15、beneciation has been carried out this way for many years because of the known poor oatability of the ultranes and because in the past it has been determined that the larger phosphate bearing par- ticles oat and concentrate more efciently in the absence of ultra- nes. After the ultranes have been sep

16、arated they are typically discarded and stored in large slimes ponds as tailings, effectively becoming lost revenue to the mining operation.Legend International Holdings Inc. major phosphate deposits Paradise South and DTree are known to average between 20 wt% and 60 wt% ultrane particles, containin

17、g up to 55 wt% of the phos- Corresponding author.E-mail address: .au (A.J. Teague).0892-6875/$ - see front matter Crown Copyright 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2011.12.007Contents lists available at SciVerse ScienceDirectMinerals Engineeringj

18、ournal homepage: www. /locate/ minengA.J. Teague, M.C. Lollback / Minerals Engineering 2728 (2012) 525953conditioning and otation and depressants for Fe2O3 and Al2O3 rejection. Prior to otation, 1.5 kg of dry solid was wet-ground for 2 min in a 7 l laboratory rod mill at 63 wt% solids us

19、ing distilled water, until a particle size distribution of 80 wt% passing 150 lm was achieved. The slurry was then wet screened at 150 lm and 20 lm, so that the +150 lm oversize and 20 lm ultranes were re- moved respectively. This left 1 kg of solid ( 150 lm + 20 lm frac- tion) available for otation

20、. The slurry was dewatered to 75 wt% solids for conditioning, using a pressure lter. High intensity conditioning was carried out by vigorously agitating the solids and reagents in a 1 l stainless steel ask, at 1100 rpm, using a drill press with impellor. Soda ash (Na2CO3) was added to the slurry at

21、a dose of0.8 kg/t and stirred for 2 min until a pH of between 9.3 and 9.5 was achieved. Tall oil fatty acid and diesel were then added together as an emulsion at a dose of 1.3 kg/t (ratio of 1:1) and the slurry stirred for a further 6 min. When the amount of Fe2O3 in the feed was known to be 4% by w

22、eight or greater, guar gum depressant was added to the slurry as a 1 wt% solution and stirred for a further 2 min. After conditioning, each sample was diluted to 30 wt% solids with distilled water and transferred to the otation cell.Batch otation was conducted in an aerated 2.5 l Denver ota- tion ce

23、ll, with a constant impeller speed of 1000 rpm. Froth was scraped at a constant rate during rougher/scavenger otation until the froth was barren; on average, this took about 4 min. The com- bined rougher/scavenger concentrate was then re-oated in a cleaning stage using the same otation cell, without

24、 any further re- agent or water addition. The otation products were dried, weighed and assayed for P2O5, Fe2O3, Al2O3, CaO, MgO and SiO2 by ICP and XRF so that otation recoveries could be calculated.2. TheoryExamples of methods of desliming and their importance to effective recovery are discussed by

25、 Ahmed (2007). The use of screens or hydrocyclones to deslime the crushed ore dramatically improves the efciency of otation but in many cases the loss of phosphate nes is over 15% of the total phosphate. A technical re- port by Luttrell (2004) explains that beneciation plants in Florida, one of the

26、major areas for phosphate beneciation in the USA, typ- ically wash and deslime ore matrix at 150 mesh (105 lm) so that ner than 150 mesh particles are considered tailings and pumped to settling ponds so that approximately 30% of phosphate con- tained in the original ore is lost to tailings ponds. Th

27、us, while o-tation is a very effective method for the beneciationofphosphate, there remains a need for a process which can recover a portion of nes normally discarded as tailings.There is some reference in the literature to the otation of ultra- ne phosphate with column cells such as that practised

28、at the Bar- reiro concentrator in Brazil (Wyslouzil, 2009; Wyslouzil et al., 2010) however there are some drawbacks to this process. The feed to the ultrane circuit has a particle size of 100% passing 30 lm and is deslimed again at approximately 510 lm where 60 wt% of the P2O5 is still discarded. Al

29、so, of the 40 wt% of the P2O5 that is fed to the CPT otation columns, only 7 wt% is recovered to amarketable concentrate grade of 33.5%P2O5and 33 wt% is dis-carded as the otation tailing. It can be seen that this process still has major limitations of; not being able to treat and recover ultra- ne p

30、articles in the range of 010 lm; and having to install addi-tional desliming and otation circuits for a low additional mass recovery of P2O5. The method discussed in the current paper does not have these limitations.Jameson cell otation machines have a number of attributes which have made them a pop

31、ular choice for facilitating the ota- tion of ne particles in base metal and coal operations. These have been well described and documented in the past by Jameson et al. (1988) and Young et al. (2006) and others. The average air bubble size is 300 lm compared to 1000 lm for conventional otation mach

32、ines and the total surface area of 1 mm3 of air is 20 mm2 com- pared with 6 mm2 for conventional machines. This larger bubble surface area generated by the Jameson cell increases the probabil- ity of particle-bubble collision and attachment when oating ne particles. It has been documented in the pas

33、t that ne and ultrane particles exhibit improved otation characteristics when oated with small bubbles (Nguyen and Schulze, 2003; Fillipov, 1998), since the collision efciency increases and there is an increased chance of particle-bubble attachment.Although conventional and column cells have been us

34、ed before in phosphate otation, there is no reference in the literature to Jameson cells ever being used. This is surprising, given they have been used for some time in potash processing (Eisner, 2010) and they are considered to be better suited to the otation of ne par- ticles than both conventiona

35、l and column cells since they generate smaller bubbles. With the development of Legends process to oat the ultrane phosphate, it was thought there would be merit in tri- alling the Jameson cell, because of its known success in the miner- als industry and its ability to generate small bubbles and rec

36、over ne particles.3.2. Laboratory pilot plant testsContinuous otation tests using drill core and RC chip samples with highly variable mineralogy from the Paradise South and DTree deposits were carried out at laboratory pilot scale. For these tests, the 20 lm ultrane fraction was not removed from the

37、 ore samples prior to conditioning and otation. Samples of between 30 kg and 50 kg each were tumbled in a tumble mill for 15 min and screened at 25 mm to remove oversize silica. Each sample was wet-ground in a 95 l rod mill with de-ionised water at 63 wt% solids to achieve a particle size of 80 wt%

38、passing 150 lm, thickened to 75% solids by ltration and conditioned using the same reagent scheme as described in Section 3.1.After conditioning, the slurry was transferred to a bafed 300 l drum and diluted to between 15 and 20 wt% solids using de-ion- ised water for otation in a L150 (6 m high) Jam

39、eson cell. The slur- ry was continuously fed to the Jameson cell, at a constant ow rate of 0.35 m3/h, for rougher otation. Air to the cell was adjusted to create a vacuum of between 15 and 20 kPa, which produced a feed pressure of between 120 and 150 kPa. When the operation was sta- ble at the set p

40、rocess conditions, a survey was conducted by col- lecting 5 l feed, concentrate and tailing slurry samples. When the rougher stage was completed, the tailing was collected and fed continuously to the Jameson cell at 0.35 m3/h, to simulate scaven- ger otation. Surveys were again conducted upon reachi

41、ng stable operation. After the scavenger stage, the Jameson cell was drained and cleaned, and the rougher and scavenger concentrates were col- lected and fed though the cell to simulate cleaner otation. The enrichment ratios for each otation stage were found to vary with feed grade; typically they a

42、veraged between 1.8 and 2.7 for the rougher, 3 and 5 for the scavenger and between 1 and 1.5 for clea- ner otation. Similar to the bench scale tests, no further reagent additions were made to the scavenger and cleaner otation stages. The otation products were each dried, weighed and assayed for P2O5

43、, Fe2O3, Al2O3, CaO, MgO and SiO2 by ICP and XRF so that o- tation recoveries could be calculated.3. Materials and methods3.1. Bench scale conventional otation cell testsBench scale studies were carried out on two of Legends phos- phate deposits, Paradise South and DTree, to determine the effect of

44、ultranes removal, pulp density and water quality during54A.J. Teague, M.C. Lollback / Minerals Engineering 2728 (2012) 5259During operation of the Jameson cell, only one problem was encountered with short-circuiting. Occasionally the feed pressure to the cell would drop due to airlocks in the pump c

45、aused by excess froth in the slurry. When this occurred, it was necessary to stop- start the pump so that the feed pressure and vacuum in the down- comer were restored. Although this problem was encountered occasionally, it was quickly managed and did not affect the ota- tion results.conditioning at

46、 low wt% solids yields poor P2O5 recoveries and grades. The P2O5 recoveries increase from a low 10.3% at 30 wt% sol- ids to a high of 97.8% when the slurry is conditioned at 75 wt% solids. There is not much difference in concentrate grade when the slurry is conditioned at 51 or 75 wt% solids but the

47、 P2O5 recovery is over 50% greater when conditioned at 75 wt% solids indicating that the hydrophobicity of the P2O5 in the feed has increased markedly under these conditions, resulting in improved oatability. Gruber et al. (1995) explain that the benets of conditioning at high wt% solids are twofold

48、; rstly, it increases the concentration (moles per litre) of the collector and therefore the force driving chemisorption of col- lector onto phosphate is increased and secondly, the effects of dis-3.3. MineralogyPhosphorite at Legends DTree deposit occurs predominantly as mudstone and silty mudstone

49、 phosphorite (also known as micros- phorite) with some minor occurrences of peloidal grainstone phos- phorite (also known as pelletal phosphorite). At Paradise South the phosphorite is made up of pelletal phosphorites almost completely comprised of collophane (carbonate uorapatite), mudstone phos- p

50、horite and replacement phosphorite, which is a more indurated, porcellanous phosphorite (Hough, 2010). Mineralogical studies of DTree and Paradise South ore by QEMSCAN (Jones, 2011) and quantitative XRD (Johnson, 2009) determined the major mineral species to be apatite, quartz, kaolinite and goethit

51、e. Average head assays taken from the test samples that were used in this study for DTree and Paradise South ore are given in Table 1.Ca2+Mg2+solved cations such asandare reduced when thequantity of water is reduced so that less reagent is lost due to bulk precipitation and there are fewer cations a

52、vailable to activate quartz. The results in Table 3 conrm this hypothesis.4.3. Effect of water qualityFurther to the discussion in the previous Section 4.2, the study undertaken by Jacobs Engineering (Gruber et al., 1995) clearly showed that the use of distilled or de-ionised water in phosphate cond

53、itioning and otation, instead of plant or tap (hard) water, in- creased the recovery of phosphate and reduced the recovery of quartz. They suggested that the Ca2+ ions in the hard water acti- vated the quartz and residual oleate ions from the collector were physically adsorbed onto the quartz in the

54、 otation cell. In the cur- rent study, bench scale tests were carried out using DTree ore to conrm this effect and the results are given in Table 4, whilst Fig. 1 shows a plot of water hardness as CaCO3 equivalent versus P2O5 recovery. The results demonstrate that the otation recovery of P2O5 is inv

55、ersely proportional to the hardness of the water that is used in grinding, conditioning and otation, for instance 97.6% P2O5 recovery for distilled water with 1 mg/L hardness and only 59.9% P2O5 recovery for fresh site water with 410 mg/L hardness. Interestingly, the result for Test 4 of 97.1% P2O5

56、recovery using IX softened site water, conrmed that the ion-exchange apparatus successfully removed hard cations to a level 0.1 mg/L hardness, making it similar in quality to distilled water. The P2O5 grade of the concentrates was found to increase from 26.6% P2O5 to 30.9% P2O5 as the water hardness

57、 decreased, although this did not appear to be as linear as the relationship between water hardness and P2O5 recovery as illustrated in Fig. 1. When hard water was used during conditioning, a pH change in the slurry was observed, although more soda ash was needed to raise the pH from approx- imately

58、 eight to the target of between 9.3 and 9.5 and hence neu-4. Results and discussion4.1. Ultranes removal conventional otation cell testsTable 2 shows results that were obtained from bench scale o- tation tests on DTree ore using a conventional Denver cell, with and without ultranes. These tests were designed to investigate and conrm the effect ultrane particles have on P2O5 concentrate grade and recovery when oated at different pulp densities.It ca