Esan Eczacıbaşı Milas feldspat Tesisi albit konsantrelerinin flokülasyon davranışları

Abstract

Sıvı içindeki küçük katı taneciklerin, çökebilecek veya süzülebilecek büyüklükte flok oluşturması amacıyla yapılan flokülasyon işlemi, başta cevher ve kömür hazırlama tesisleri olmak üzere pek çok endüstriyel üretimde ve atık suların iyileştirilmesinde oldukça yaygın uygulama alanı bulmaktadır. Bu çalışmada, Esan-Eczacıbaşı Milas Albit tesisindeki -20 um boyutundaki albit konsantresinin flokülasyon özellikleri ve albit-noniyonik polimer sisteminin adsorpsiyon mekanizması ile ilgili deneysel çalışmalar yeralmaktadır. Flokülasyon parametrelerinin -20 um boyutlu albit konsantresinin çökmesine etkisinin incelendiği deneysel çalışmalarda, pülpte katı oranı, flokülan tipi ve miktarı ile pH değişimi birer parametre olarak incelenmiştir. Bu grup deneysel çalışmalar sonucunda, verimli bir albit flokülasyonu için en uygun şartların % 20 pülpte katı oranı ve 20 g/ton N-300 polimerinin kullanımı ile sağlandığı belirlenmiştir. Flokülan ilavesi olmaksızın 15 dakikada tamamlanabilen çökme, flokülan kullanımı ile ilk 5 dakikada tamamlanırken, pH değişiminin albit flokülasyonu üzerinde net bir etkisi gözlenememiştir Saf albit numunesi ile albitin çözünme kinetiğinin belirlenmesi amacıyla yapılan deneysel çalışmalar ve zeta potansiyeli ölçümleri ise albit süspansiyonunun asidik ve alkali ortamlara karşı kuvvetli şekilde tamponlandığını, albit mineralinin sıfır yük noktasının pH: 2'nin altında olduğu göstermiştir. Farklı polimerlerle yapılan zeta potansiyeli ölçüm sonuçlarında ise en efektif polimerin yüzeyi en az negatif yapan N-300 olduğu saptanmıştır. Albit / Noniyonik polimer mekanizmasını belirleyebilmek amacı ile yapılan adsorpsiyon ve desorpsiyon/deneylerinde, adsorpsiyon zamanı, katı içeriği, pH değişimi ve polimer konsantrasyonu birer parametre olarak incelenmiştir. Zeta potansiyeli ve adsorpsiyon deneylerinden elde edilen verilere dayanılarak albit /noniyonik polimer bağlanma mekanizmasının hidrojen bağı üzerinden olduğu belirlenmiştir. Albit flokülasyonuna etki eden diğer parametrelerin incelendiği deneysel çalışmalarda ise flokülasyonda kullanılan suyun çökmeye net bir etkisi gözlenemezken, flokülasyon pülpünde oleik asit varlığının flokülasyon şartlarını nispeten kötü leşti rd iğ i gözlenmiştir.

Albite (NaAISi308), one of the minerals in the plagioclase feldspars series, is characterized by a luster appearance with white and gray colors, less frequently greenish and yellowish. Albite is usually found together with quartz, mica, and sometimes iron oxides, rutile, and turmaline. Feldspars is principally used in the manufacture of glass and ceramics as a flux or source of alumina. Beneficiation of albite is primarily accomplished by a number of separation methods including magnetic, electrostatic and flotation. Although the concentration scheme is usually dependent on the quality of the end product, flotation is almost invariably the most popular beneficiation method. While anionic collectors such as oleic acid is used to collect colored impurities, e.g., iron oxides and rutile, cationic colectors are used to float feldspar at pH 2 while depressing quartz with HF. Esan-Eczacıbaşı Milas Albite concentrator produces glass and ceramic quality albite with a production capacity of 200,000 t/y. The ore is reduced to -0.5 mm in size and a fatty acid type collector is used to float the colored impurities at pH 8- 10. The minus 0.5 mm flotation concentrate is then passed through a combination of hydrocyclone/spiral classificator to obtain three products, i.e. 0.5x0.1 mm, 0.1x0.02 mm and -0.02 mm. The latter two products are fed into the settling cones where the solids is densified with the aid of floccullants followed by dewatering by disc filters. The overflow is recirculated back to the plant after it is clarified. Investigations in the plant have revealed that the flocculation regime used in the dewatering circuit is not appropriate and thus leads to slow settling rates and in turn to inefficiencies in the plant operation. No literature of relevance was found on the subject of albite flocculation. It is therefore the objective of this study to test the performance of various acrylamide based polymers in settling the minus 20 urn albite concentrate and find out the optimum operating conditions. Towards this aim, a systematic study has been also initiated to understand the way albite interacts with nonionic polymer. The sample used in the flocculation tests was collected from the fine (-20 urn) settling cone product in the Esan-Eczacibaşi Albite concentrator. The chemical composition of the sample is presented in Table 1. Table 1. Analysis of -20 n,m albite concentrate Ultrapure albite crystals received from the same deposit was ground in an agate mortar to obtain a sample of -74 (am in size. This sample was used for both adsorption and zeta potential measurements. While experiments associated with pure albite were conducted in distilled water, the actual plant water was used in the flocculation tests. The anionic (A120, A95, and A130), cationic (C521, C528), and nonionic (N- 100, N-200 and N-300) flocculants were all received from Cytec Chemical Co. and specified to have molecular weights of 3-15x10, 3-4x10, and 3-4x10, respectively. Tannic acid, NaCI, NaOH and HCI were all Fluka made certified chemicals. The flocculation tests were performed in a one liter graduated cylinder. The settling teste, apart from studies on solids concentration, were done by adding 200 g of - 20 [im material into the cylinder, mixed thoroughly and falling of the interface height was recorded as a function of time. Zeta potential measurements were conducted by means of Zeta Meter 3.0 which is equipped with a microprocessor unit capable of directly measuring the average zeta potential and its standard deviation. 100 mg - 20 u.m pure albite was added into 100 ml of distilled water and conditioned for 10 min. The suspension was kept stationary for 3 min. and the average of ten particles was taken as the zeta potential. Details of the measurement procedure is given elsewhere Adsorption tests were carried out in 20 ml-glass scintillation vials. 1 g of - 20 jam pure albite was added to 15 ml of polymer solution of desired concentration. The suspension was conditioned for 1 hour and the solids were filtered out. The supernatant was subjected to polymer analysis. Polymer analysis was made by a nephelometric method developed by Attia and Rubio (1975) for low concentrations of polyethylene oxide and polyacrylamide flocculants. A series of nonionic polymer solutions of known concentrations (5ml) in the range of 0-3 parts/10 (ppm) were treated with 40 ml of 0.1 M NaCI solution and 5 ml of 0.1 % tannic acid solution in 50 ml volumetric flask. The mixture was shaken for 1 h and the turbidity of the resultant solution was measured by a Shimadzu UVA/is spectrophotometer at 625 nm wavelength. The XI linear portion of the calibration curve, in the range of 0.5-2.5 mg/kg, was used for calculating the residual polymer concentrations Figure 1 presents the height of the interface in the absence of polymer as a function of time at different pulp densities as defined by percent solids by weight. The plant water was used as the medium at its natural pH. It is apparent that as the pulp density increases the settling rate, as defined by the initial slope in the sedimentation curve, and also the interface height decrease. Despite higher sedimentation rates at low pulp densities, considering both conditions at the plant and economic capacity of the operation, 20 % pulp density was considered suitable for performing the subsequent flocculation tests. It is also evident in Figure 1 that most of the sedimentation occurs during the first 15 min. of the settling for all pulp densities. However, it is interesting to note that, in the absence of any polymer addition, the upper portion of the suspension appeared to be rather hazy indicating that under natural conditions a long retention time is required to achieve a clear supernatant. H m < 20 40 60 TIME, min 80 100 Figure 1. Settling behavior of -20 urn albite concentrate against time in the absence of flocculant at different pulp densities. XII Figure 2 illustrates the effect of various type of flocculants on the elapsed settling time as determined by the interface height. The amount of polymer is 5 g/t for all polymers used. Compared to the anionic and cationic polymers, the nonionic polymers yields the best settling condition. The settling rate further increases with increasing the degree of nonionicity. Figure 2 further shows that the settling time is drastically reduced in the presence of polymer. Settling is almost over in less than five min. The same improvement was observed in the supernatant as the cloudiness was substantially reduced in the order of effectiveness shown in Figure 2. A similar enhancement was also noted upon increasing the amount of polymer up to a certain concentration above which restabilization of the suspensionwas observed as reported in most flocculation studies. Figure 3 exhibits the settling behavior of albite in the absence and presence of polymer as a function of pH. It is clear that, due to scattering, no significant effect of pH is apparent both in the presence and absence of polymer. H O 5 10 15 AMOUNT OF POLYMER, g/ton 20 Figure 2. Variation of interface Height With The Amount Of Polymer For -20 |im Albite Concentrate Upon 5 min. of Settling Time XIII Figure 3. Settling Behavior Of -20 ^m Albite Concentrate Vesus pH With Different Flocculants (settling time : 5 min, polymer concentration : 5 g/t) The plagioclase feldspars form a complete solid-solution series from pure albite (NaAISi308) to pure anorthite (CaAİ2Si20s). Considerable potassium may be present toward the albite end of the series. Therefore, it is more likely that albite should be written as (Na,K)AISi308. The dissolution behavior of albite has been systematically studied that the rate of hydrolysis of feldspar is highly pH dependent and results from the following reactions: At low pH < 2.9 (H30)AISi308 + H+ = (H30)AISİ307(OH)+ (1) At intermediate pH (2.9-8.0) (Na,K)AISi308 + nH20 = (Na,K)AISi308 (H20)n (2) At high pH > 8.0 (Na,K)AISi3O7+0.4OH =(Na,K)AI(OH)fj.4Si308 0.4- (3) XIV Stumm and Morgan based suggest that factoral orders on H and ligands given in Eq. 3 are compatible with a direct dependence on the degree of surface protonation or on the concentration of ligand surface complexes. This hypothesis is further supported by the fact that the volume occupied by alkali ions in albite is rather small compared to the large H3O. The most important factors affecting the rate of dissolution of albite are pH and the concentration of dissolved Al. The rate dependence on pH exhibited remarkable similarities to the solubility curves of Al compounds and also Al showed the largest inhibiting effect on the dissolution rate. Figure 4 presents the dissolution kinetics of albite in water as a function time at initial pH values of 3, 11, and natural. The natural pH of albite was found to be 8.1. When the suspension is mixed with distilled water of about pH 6, it takes approximately 15 min. for albite mineral to reach its equilibrium pH of 8.1. When the initial pH is adjusted to 3 or 11 it takes about 15 min. to approach one pH unit to the natural pH but several additional hours to reach its equilibrium pH. In other words, albite suspensions are buffered relatively strongly in both acidic and alkali media. This feature becomes important in the interpretation of adsorption results. Albite, as most other silicate minerals, exhibit negative zeta potentials throughout the practical pH range of 2 to 12. The zero point charge (zpc) of albite is roughly between 1 and 2, as shown in figure 5. This is in line with the zpc of many silicate minerals including quartz. However, no electrokinetic data on albite was found in the literature. xv Figure 4. Dissolution Kinetics of Pure Albite in Water at Different The zeta potential of albite as a function of N-300 nonionic polymer concentration is given in Figure 6. The zeta potential gradually decreases with increasing N-300 concentration, i.e. it becomes less negative. The albite suspension was found to flocculate at 1 mg/kg N-300 concentration and measurements became increasingly difficult above this value. The dependence of pH on zeta potential of albite in the presence and absence of different nonionic polymers is presented in Figure 7. It is clear that the addition of polymer makes the surface of albite less negative at all pH values with N-300 being the most effective. This indicates that as the nonionicity increases more of negative charges on the albite surface are tied up with the polymer. Figure 3 exhibits the settling behavior of albite in the absence and presence of polymer as a function of pH. It is clear that due to scattering no significant effect of pH is apparent both in the presence and absence of polymer. XVI Figure 8. Dependence of Adsorption of 10 mg/kg N-300 on Albite Against Conditioning Time at Natural pH. Since pH was pointed out as an important parameter in the dissolution of albite, the dependence of adsorption of N-300 was studied as a function of pH. This is shown in Figure 10. Evidently, the adsorption density increases with increasing pH and reaches a constant value above pH 9 where it becomes difficult to adjust pH. Adjusting the initial pH of the solution to pH 12 resulted in a pH value of 9.3. High adsorption density neutral and high pH correlates well with the flocculation and settling tests discussed previously. Adsorption isotherm of N-300 onto albite is presented in Figure 1 1 where the adsorption density is plotted against the residual polymer concentration. Adsorption is found to increase with an increase in polymer concentration and reaches a plateau value at about 10 mg/kg N-300 concentration. Athe adsorption isotherms appears to be of a typical Langmuir type. Figure 5. Zeta Potential of Albite as a Function of pH in Water Figure 6. Variation of Zeta Potential with N-300 Concentration Figure 5. Zeta Potential of Albite as a Function of pH in Water Figure 6. Variation of Zeta Potential with N-300 Concentration Since albite is a sodiun form of silicate mineral and the polymer is nonionic, it appears that hydrogen bonding is the only plausible mechanism in the system. As a shown in Equations 1 through 3, albite acquires a positive charge below pH 2.9 and thus is not as much amenable to adsorption of N-300. Above pPH 3, adsorption progresively increases due to formation of silanol groups and reaches its highest level above pH 8, where additional negatively charged surface complexes form. Tthe decrease in the zeta potential of surface with the addition of polymer shown in Figures 6 and 7 is in agreement with the above explanation. It appears that positive sites are depleted upon addition of the polymer. XXII Figure 5. Zeta Potential of Albite as a Function of pH in Water Figure 6. Variation of Zeta Potential with N-300 Concentration Since albite is a sodiun form of silicate mineral and the polymer is nonionic, it appears that hydrogen bonding is the only plausible mechanism in the system. As a shown in Equations 1 through 3, albite acquires a positive charge below pH 2.9 and thus is not as much amenable to adsorption of N-300. Above pPH 3, adsorption progresively increases due to formation of silanol groups and reaches its highest level above pH 8, where additional negatively charged surface complexes form. Tthe decrease in the zeta potential of surface with the addition of polymer shown in Figures 6 and 7 is in agreement with the above explanation. It appears that positive sites are depleted upon addition of the polymer.