2009-empirical uation of the role of sodium silicate on the separation of silica from jordanian siliceous phosphate

1、Separation and Purication Technology 67 (2009) 289294Empirical evaluation of the role of sodium silicate on the separation of silica from Jordanian siliceous phosphateS. Al-ThyabatFaculty of Mining and Environmental Engineering, Al-Hussein Bin Talal University, P.O. Box 20, Maan, Jordana r t i c l e

2、i n f oa b s t r a c tArticle history:Received 1 December 2008Received in revised form 17 March 2009 Accepted 18 March 2009The role of sodium silicate as depressant/dispersant on siliceous phosphate otation was empirically evaluated. Factorial experimental design was used to investigate the effect o

3、f sodium silicate and its interactions with collector dosage and feed characteristics on phosphate recovery and silica depression. Analysis of variance (ANOVA) conducted on otation results of unslimed feed showed the existence of synergistic effects between collector, sodium silicate and feed charac

4、teristics (P80) which emphasise the necessity to design a reagent suite for each specic feed characteristic. 2009 Elsevier B.V. All rights reserved.Keywords:FlotationPhosphate separation Sodium silicate Siliceous phosphate Jordanian phosphate1. IntroductionGong et al. 13 provided an explanation of t

5、he mechanism of action of sodium silicate on depressing iron oxide in apatiteiron oxide mixture. Using different models of equilibrium for silicate species in the solution and XPS to study the adsorption of sili- cate species on both surfaces of hematite and apatite, the authors reported that the me

6、chanism of action of sodium silicate is mainly due to the presence of polymeric silicate species and small colloidal silica particles in otation pulp. They alsoconcluded that polymeric silicate species have a stronger depressing effect than monomeric silicates and colloidal amorphous silica particle

7、s.Furthermore, the study of solution chemistry of sodium silicate with some of salt type minerals conducted by Hu et al. 14 showed that the depression mechanism of these calcium bearing miner- als by sodium silicate depends on the solubility limits of calcium silicate on the solution which in turn d

8、epends on the concentra- tion of sodium silicate and solution pH. In order to depress apatite and calcite, a sufcient amount of sodium silicate need to be pre- cipitated/adsorbed on the apatite and calcite surface. For sodium silicate concentrations similar to those used in otation, the critical pH

9、(pH where signicant amount of sodium silicate precipitations occurs) is about 11.5 for apatite and 9 for calcite which indicate that precipitation of calcium silicate on calcite is higher than apatite. The authors also reported that sodium silicate addition signicantly reduces iso-electric point (ie

10、p) of calcite (from pH 10 to 7) where the effect on apatite was negligible which suggested that sodium silicate depression effect on apatite is limited on the pH range used for phosphate otation (8.59.5).Recently, Lietal.15 studiedthe effectofusingacidiedsodium silicate as depressant and dispersant

11、in bitumen extraction from the Canadian oil sands. The authors concluded that the benecialSodium silicate (SS) is commonly used in depressing carbonates and siliceous gangue in otation of sparingly soluble and salt type minerals such as apatite, calcite, and uorite. According to the lit- erature 16,

12、 some of the benecial effect of sodium silicate in phosphate otation when fatty acid is used as collector are the removal of calcium cation by precipitating them as calcium silicate, froth stabilisation, and improving phosphate otation rate.The mechanism of minerals depression is mainly due to the h

13、ydrolysis of sodium silicate solution which produces a num- ber of monomeric, polymeric and colloidal species. The role of each species on the depression mechanism was studied by some researchers 711. These studies showed that the polymeric sodium silicate solution has more depression effect due to

14、the abil- ity of the polymer to cover larger surface of the mineral due to its weight and size.Zhou and Lu 12 studied the mechanism of acidied sodium sil- icate (ASC) in depressing calcite in uorite otation when oleic acid was used as collector. They summarised the mechanism of action of ASC as foll

15、ows:(1) Promoting the dissociation of calcium ion from calcite which reduces the consumption of oleic acid consumption by calcite.(2) Complexation with calcium ions in the pulp which reduce theirnegative effect on otation mechanism.E-mail address: .jo.1383-5866/$ see front matter

16、 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.03.034Contents lists available at ScienceDirectSeparation and Purication Technologyjournal homepage: /locate/seppurS. Al-Thyabat / Separation and Purication Technology 67 (2009) 289294290effect of using acidied sodium

17、 silicate could be summarised asfollows:(1) Precipitating divalent cations (e.g. calcium and magnesium) from process water which preventing their deteriorating effect in bitumen extraction.(2) Maintaining an adequate pulp slurry pH for better bitumen extraction.(3) Dispersing/depressing clay nes fro

18、m otation by its long chain polymeric species resulted from sodium silicate acidication.Some researchers 1619 studied the kinetics and chemistry of phosphate otation from its siliceous gangue by fatty acids. Most of these studies emphasised that the formation of calcium dioleate by the reaction betw

19、een apatite and oleate is responsible for the chemisorptions of collector on the apatite surface. However, the presence of calcium divalent in the otation pulp either by the dis- solution of apatite or due to the process water, precipitate more calcium oleate on the surface of the silica (gangue) wh

20、ich activate it andrenderithydrophobic. Thestudyrecentlyconductedby Brown et al. 20 showed that the maximum hydrophobicity of the silica occurs when excess collector (2:1 oleate to calcium) is present in the solution. This may emphasis the role of sodium silicate in depress- ing silica by precipitat

21、ing some of the solution calcium cations as calcium silicate.In the current work, more light will be shed on phosphate otation performance using different sodium silicate dosages. Full factorial experimental design were used to evaluate the interaction of collector, sodium silicate and feed size on

22、otation recovery and grade. Flotation feedusedinthis study were asreceived (nodeslim- ing) feed which apposed to most of the previous work reported in the literature.Fig. 1. Size analysis of the main feed (P80 = 580 m).Table 2Chemical and physical analysis of the reconstructed feeds.then conditioned

23、 for another 3 min. Then the pulp was diluted to 25% solids and impeller speed increased to 1200 rpm. Flotation were started and continued till barren froth was obtained. Approx- imately, otation time were 3kg/ToF). On the other hand concentrate grade (%P2O5) was notTable 1Chemical analysis of the m

24、ain feed.Fig. 2. Size parameters (P20, P50, and P80) of the reconstructed feeds.Upper limit ( m)%P2O5%Insol100029.616.4285029.517.4871022.836.8650017.949.935522.235.0825029.618.4418030.412.1412528.715.29026.719.887526.620.685326.418.664526.917.523826.318.22Feed no.P80 ( m)P50 ( m)P20 ( m)%P2O5%Insol

25、Main feed58039023023.532.7#145025016525.826.1#248038526022.435.5#359035525523.734.2#464050035523.632.9S. Al-Thyabat / Separation and Purication Technology 67 (2009) 289294291Fig. 3. The effect of sodium silicate dosage on otation recovery and grade (Feed #4, tall oil = 5 kg/ToF).ondly, the reaction

26、between calcium ions in the solution (due to apatite dissolution, or process water) with the collector which caus- ing calcium dioleate to precipitate on apatite surface and render it hydrophobic (physisorption).Therefore, the presence of slimes and the coarse nature of the feed consume some of the

27、tall oil and reduce its adsorption on apatite surface by either chemisorptions or physisorption. The addition of sodium silicate had two effects, rstly disperse ne particles in the pulp and hence reduce the consumption of tall oil and secondly depress silica particles by the adsorption on its surfac

28、e. At higher sodium silicate dosages, calcium silicate pre- cipitation increased which reduced the apatite recovery by two methods: rstly, consuming calcium ions from the solution which in turn reduces the reaction rate between apatite and the collector (chemisorptions) andsecondly, increasingbulk p

29、recipitation ofcal- cium silicate in the solution may increase the possibility of calcium silicate precipitation on apatite surface which reduce its selectivity to the collector.Concentrate gradebehaviourasshownin previous gures, indi- cates that the low recovery of apatite is mainly due to the poor

30、 interaction between the collector and apatite surface either because of no sufcient collector, slime coating of apatite surface, or due to high inertia of coarse apatite particles. This may indicate that the main role of sodium silicate in otation of this type of feed is to increase selectivity of

31、apatite by dispersing ne particles and clean up apatite particles surface from ne silica particles possibly attached to them by electrostatic forces.Fig. 4. The effect of sodium silicate dosage on otation recovery and SE (Feed #4,tall oil = 5 kg/ToF).signicantly affected by the increase in sodium si

32、licate dosage. %P2 O5 Conc%P2O5 conc. max%Insolconc%InsolfeedSE (%)= 100 100(1)At this high collector dosage (5 kg/t), it is expected to obtain higher recovery on both low and high sodium silicate dosage. To explain this, it is well known that there are two proposed meth- ods in which the collector

33、(oleate) and apatite can be interacted 1,14: rstly, formation of calcium dioleate by the reaction between calcium sites on apatite surface and oleate i.e. chemisorption. Sec-3.2. Collector and sodium silicate interactionIn order to evaluate the interaction between the collector and sodium silicate d

34、osage, mixed factorial design (2 levels for sodiumTable 3Collector and sodium silicate dosage interaction (Feed #2).Sodium silicate: low (L), 4.5; high (H), 23; Tall oil: low (L), 2.2; medium (M), 3.8; high (H), 4.2.Exp no.Tall oil (kg/ToF)Sodium silicate (kg/ToF)%Recovery%P2O5Separation efciency, S

35、E (%)1LL31.930.443.22ML33.430.042.63HL4LH5MH61.229.630.36HH58.129.732.3S. Al-Thyabat / Separation and Purication Technology 67 (2009) 289294292Fig. 7. Collector dosage and sodium silicate dosage interaction effect on SE (Feed #2).Fig. 5. Collector dosage and sodium silicate d

36、osage interaction effect on otationrecovery (Feed #2).phosphate particles to the collector. The higher collector dosage at lowsodium silicate compensate for excess consumption of collector byslimeswhichincrease phosphaterecoveryasexpected. However, separation efciency, concentrate grade results indi

37、cate that even though higher sodium silicate dosage increases the recovery it also increases the recovery of gangue (silica) to the concentrate. This may be explained by the increase of ne silica particles dispersed by sodium silicate entrainment to the concentrate.Analysis of variance (ANOVA) analy

38、sis of the previous results showed that both of collector and sodium silicate dosage and their interactions are signicant for otation recovery, and separation efciency. On the other hand, concentrate grade are not affected by the change of these parameters and their interactions. F-Values also showe

39、d that collector dosage and its interaction with collec- tor dosage was more signicant than changing collector dosage which emphasis the synergistic effect between chemicals used in phosphate otation.3.3. Collector, sodium silicate, and feed size interactionFig. 6. Collector dosage and sodium silica

40、te dosage interaction effect on concentrate grade (Feed #2).Two level, (23) factorial experimental design was used to inves- tigate the effect of interactions between feed size, collector, and sodium silicate on otation performance. The experimental results are as shown in Table 4 while ANOVA analys

41、is results are shown in Tables 57.ANOVA analysis of otation recovery showed that all the stud- ied parameters and their interactions are signicant on otation recovery. Comparing the F-value of these parameters, feed size represented by P80 is the most signicant parameter followed by the collector do

42、sage. On the other hand, the interaction between sodium silicate and collector dosage is the least signicant param- eter. Most interesting, the third interaction between parameterssilicate and 3 levels for the collector) were used. The results are shown in Table 3 and Figs. 57.Phosphate recovery at

43、high sodium silicate dosage was signi- cantlyhigher than that atlowdosage. Asignicant improvement of otation recovery was noticed at high collector and low sodium sil- icate dosage. On the other hand, SE for both low and high collector dosages was low for this type of otation feed.These results supp

44、orted the previous claim that the main role of sodium silicate for this unslimed feed is to disperse ne particles which reduce collector consumption by slimes and expose moreTable 4Feed size, collector dosage, and sodium silicate interaction.Feed size: low (), 450; high (+), 590; Sodium silicate: lo

45、w (), 4.5; high (+), 23; Tall oil: low (), 3.8; high (+), 4.2.Exp no.Feed size (P80, m)Sodium silicate (kg/ToF)Tall oil (kg/ToF)%P2O5%RecoverySeparation efciency, SE (%)130.281.558.62+31.833.257.13+30.778.559.84+31.448.252.35+31.273.165.96+31.921.352.47+29.580.757.18+31.620.454.0S. Al-Thyabat / Sepa

46、ration and Purication Technology 67 (2009) 289294293Table 5ANOVA analysis of otation recovery.R2 = 1 SSE/EDF.SST /DFT The main role of sodium silicate in phosphate otation is to depress the silica particles by the precipitation of sodium silicate polymericspeciesonsilicaparticles. Alsosodiumsilicate

47、interacts with calcium ions and precipitates them as calcium silicate on the solution, and on silica and phosphate particle which explain why extra sodium silicate dosage may signicantly reduce phosphate recovery. The addition of sodium silicate to this unslimed feed improved phosphate otation recov

48、ery by reducing collector consumptionby two methods: rstly dispersing the ne particle (slime), and secondly precipitation of calcium ions from the solution. All the studied otation parameters and their interactions weresignicant for otation recovery while it was not the case for otation selectivity

49、(separation efciency) and concentrate grade. This indicates that otation recovery is more sensitive for the change in otation parameters than concentrate grade and SE. ANOVA showed that interactions between otation parameters was signicant for otation recovery, grade and separation ef-ciency which s

50、upported the existence of the synergistic effects between otation chemicals and the necessity to design a reagent suite for each specic feed characteristics.Table 6ANOVA analysis of concentrate grade.Table 7ANOVA analysis of phosphate-silica separation efciency.AcknowledgmentsThe author would like t

51、o thanks the reviewers for their valuable comments and Al-Hussein Bin Talal University for supporting this work.(FS SS CD) was more signicant on otation recovery than some second interactions (FS SS & SS CD); this may due to poor tting of the model a 21 or because of the synergistic effect of chemic

52、als used in phosphate otation and feed characteristics. These results supported the wisdom of separating coarse and ne particles in otation since each feed requires a specic reagent suite.On the other hand, ANOVA analysis of concentrate grade showed that concentrate grade was less sensitive to the c

53、hange of the studied parameters. Apart from feed size and third parameters interactions, all other parameters were notsignicant.ANOVA analysis of separation efciency showed that feed size, sodium silicate dosage, and the third interaction between the stud- ied parameters (FS SS CD) are the most signicant parameters on the otation selectivity. Also the third interaction effect was more signicant than collector dosage, and other second interac- tions. This indicates that