Effect of galena grain size on flotation kinetics

Laboratory tests of relationship between kinetics of flotation of pure galena smaller than 38 μm in size and concentration of potassium butyl xanthate show that flotation rate undergoes considerable reduction when mineral grains are under 18 μm in size. Size grades below 18 μm show the slowest flotation rates that are nearly equal at the collector concentration of 0.5 mg/l. With the higher collector concentration, the flotation rate grows in all size grades under testing.     

Effect of gas rate and impeller speed on bubble size in frother-electrolyte solutions

In a flotation cell, bubble size is a function of both coalescence and breakup phenomena. Two phase tests, conducted in a conventional 5.5 L Denver mechanical flotation cell, studied the effect of impeller speed, gas flow rate and frother concentration on bubble size in various electrolyte-frother solutions. The addition of frother to a synthetic sea salt did reduce the measured bubble size (at certain mechanical conditions); whereas the effect of frother addition to NaCl was too small (when compared to measurement errors) to make significant conclusions. This led to more detailed CCC curves (0–50 ppm MIBC) for NaCl, NaCl + MgCl₂, NaCl + CaSO₄, and NaCl + KCl solutions, at constant electrolyte concentrations, to be conducted. They showed an increase in bubble size with the addition of MIBC. This was attributed to the saturation of frother at the air-water interface, reducing local surface tension gradients that help produce smaller bubbles. This occurrence is typically masked in traditional CCC curves due to the dominance of coalescence effects at low frother concentrations.     

Bubble size as a function of impeller speed in a self-aeration laboratory flotation cell

The effect of impeller speed (power consumption) on bubble size in a self-aerated Denver laboratory flotation cell was measured. The bubble size increases with increasing impeller speed. The explanation is that the accompanying increase in gas rate causes an increase in bubble size that more than offsets any effect of increasing shear.     

有机抑制剂鞣酸对黄铜矿和方铅矿浮选的影响

通过单矿物、人工混合矿、实际矿石浮选试验,吸附量和红外光谱测试,研究了鞣酸对黄铜矿和方铅矿浮选的影响及其与矿物的作用机理。结果表明,鞣酸对方铅矿具有强抑制作用,对黄铜矿浮选的抑制作用较小。当鞣酸用量为5 mg/L,浮选180 s时,黄铜矿回收率为83.30%,而方铅矿的回收率只有17.65%。吸附量测试表明,鞣酸在黄铜矿表面的吸附密度为2.03 mg/m2,在方铅矿表面能够达到6.05 mg/m2。红外光谱检测表明,鞣酸通过酚羟基与方铅矿表面发生作用,与黄铜矿作用则很弱,这正是鞣酸能抑制方铅矿的原因。     

Influence of turbulence kinetic energy on bubble size in different scale flotation cells

Although the impact of hydrodynamic conditions in a flotation cell is often evaluated by correlating impeller tip speed with bubble size, the literature reports inconsistent results, some showing a reduction in bubble Sauter mean diameter (d₃₂) with increasing impeller speed, others showing little to no effect. A review of these results indicate that cell size may be a factor where small laboratory-scale cells, smaller than 50 L, tend to support the correlation while larger machines do not. This paper demonstrates an alternative approach using the average turbulent kinetic energy (TKE) in place of the impeller speed. Results were obtained using two cells with the same geometry but different size, 5 L and 60 L. Bubble size (d₃₂) was measured using the Anglo Platinum Bubble Sizer. Local velocity and velocity fluctuation were measured using a constant temperature anemometer to estimate the average turbulent kinetic energy (TKE). The effect of impeller tip speed on d₃₂ and TKE as a function of air rate was determined. Combining the results for the two cells showed that d₃₂ initially decreased with increasing TKE to become constant above a critical TKE. The TKE region below critical was associated largely with the 5 L cell and the region above critical more associated with the 60 L cell. The inconsistent data in the literature has been explained by introducing the concept of the critical TKE and it has been confirmed that the reported effect of increasing impeller speed may have its origin in the size of the cells tested: laboratory scale cells showing an effect on reducing bubble size as TKE is below critical while large and industrial scale cells may not as TKE is above critical.     

搅拌叶轮尺寸对双叶轮浮选机性能的影响

通过对常规机械搅拌式浮选机进行改造,将其搅拌系统设计为2个转子(离心叶轮和搅拌叶轮)配1个定子的结构模式,开发了双叶轮浮选机.为了考察搅拌叶轮直径对双叶轮浮选机性能的影响,试验设计了直径为32、34和36 m m的搅拌叶轮,考察了直径对充气性能、悬浮性能和分选性能的影响.试验表明:浮选机的充气、悬浮和分选性能,与搅拌叶轮的结构特征和浮选机的转速有关.随着转速的增加,充气量越来越大,固体颗粒悬浮质量分数越来越小,而分选效率先增大后减小;在实验室现有搅拌叶轮尺寸条件下,叶轮直径为36 mm时,充气、悬浮和分选效果都达到最佳状态.     

Effect of calcium hypochlorite on the flotation separation of galena and jamesonite in high-alkali systems

Jamesonite and galena have similar flotation properties, leading to difficulties in effectively separating these two minerals by means of conventional flotation. This study assessed the depressing effect of calcium hypochlorite [Ca(ClO)₂] on the flotation separation of galena and jamesonite in high-alkali systems. Flotation test results show that galena and jamesonite have substantially different floatability in high-alkali systems. The addition of Ca(ClO)₂ depresses the flotation of jamesonite, but the depressant is unselective against galena. A flotation separation test of a mixture of galena and jamesonite was conducted. The results show that the recovery of galena and jamesonite is 92.26% and 89.75%, respectively. Adsorption measurements and infrared spectral analysis indicate that when diethyldithiocarbamate (DDTC, collector) interacts with galena and jamesonite, chemical adsorption occurs on the mineral surfaces, producing hydrophobic lead diethyldithiocarbamate (PbD₂). In a high-alkali solution, Ca(ClO)₂ exhibits little interference regarding the adsorption of DDTC on the galena surface, while it significantly inhibits the adsorption of DDTC on jamesonite. The flotation behavior of jamesonite is depressed by Ca(ClO)₂ mainly because the latter enhances the surface hydrophilicity of the former. These results provide a reference for separating galena and jamesonite concentrates prior to smelting.     

Evaluation of solids suspension in a pilot-scale mechanical flotation cell: The critical impeller speed

This paper investigates solids suspension in a pilot-scale mechanical flotation cell in terms of the critical impeller speed, N_js. Understanding solids suspension has become increasingly important in recent years due to dramatic increases in flotation cell sizes but appears to be relatively poorly researched. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension in stirred tanks, but has seldom been investigated in flotation cells. In this study, critical impeller speeds were visually determined and concentration profiles were measured through sample withdrawal in a 125 l Batequip (Bateman) pilot flotation cell. Two solids size fractions (75–106 and 150–250 μm) were tested, in ungassed and gassed conditions (J_G = 0, 1 cm/s) and at various impeller speeds (300–900 rpm). The effectiveness of solids suspension was quantified in three ways; (i) the extent of off-bottom solids suspension, (ii) the extent of axial solids distribution (suspension height) and, (iii) the variability of axial solids distribution. Consistent trends were found when these effectiveness criteria were considered against relative impeller speed, in terms of percentage of critical impeller speed, N/N_js. As per definition, off-bottom solids suspension was found to be complete at or above 100% of N_js, with significant sedimentation occurring as the impeller speed dropped below 60% of N_js. Suspension heights consistently reached a level equivalent to 90% of the tank diameter at the critical impeller speed, and dropped off significantly as N/N_js dropped below 60%. The relative standard deviation of the vertical solids distribution consistently reached a value of around 30% at N_js. The paper concludes that the critical impeller speed, as per stirred tanks, is an appropriate measure for describing and benchmarking the effectiveness of solids suspension in a mechanical flotation cell. The authors speculate that, when solids suspension is considered as a precondition to flotation, flotation cells should not be operated at specific ‘impeller speeds’ but rather at specific ‘percentages of critical impeller speed’ analogous to the ‘critical speed’ used in the operation of grinding mills.     

Effect of calcium ions and citric acid on the flotation separation of chalcopyrite from galena using dextrin

Using NaOH to adjust pH, dextrin selectively depressed galena while chalcopyrite was floated with a xanthate collector. However, when the pH was adjusted with lime, or when calcium ions were present in the pulp, the flotation of galena was “restored” while chalcopyrite was depressed in an alkaline pH, causing deteriorated flotation separations. It was found that calcium ions adsorbed preferably on chalcopyrite surfaces but not on galena, thus increasing the adsorption of dextrin on chalcopyrite. The addition of citric acid was found to eliminate the detrimental effects of calcium ions and to restore the selectivity of chalcopyrite-galena separation using dextrin.     

Effect of cuprous cyanide,dry and wet milling on the selective flotation of galena and sphalerite

Batch flotation tests of a lead–zinc sulphide composite ore from the Rosh Pinah Mine have been carried out at pH 8.5 in the presence of copper cyanide complexes. These copper cyanide complexes are often found in the recycled water that is used in the milling and the lead flotation circuits. Flotation results have shown that cuprous cyanide complexes can activate sphalerite. In addition, the activation and subsequent flotation of sphalerite was greater when the composite was dry milled as compared to wet milling. Surface analysis of copper(I)-activated sphalerite samples was studied by X-ray photoelectron spectroscopy (XPS). XPS results showed the presence of copper species on the surface of sphalerite after activation with cuprous cyanide complexes. The copper species could be removed from the surface of sphalerite after treatment with sodium cyanide. This explains, amongst others reasons, the high cyanide requirement at Rosh Pinah Mine for the efficient depression of sphalerite in the lead flotation circuit.     

A comparison of the critical impeller speed for solids suspension in a bench-scale and a pilot-scale mechanical flotation cell

This paper compares the critical impeller speed results for 6 L Denver and Wemco bench-scale flotation cells with findings from a study by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2007. Evaluation of solids suspension in a pilot-scale mechanical flotation cell: the critical impeller speed. Minerals Engineering 20, 233–240; Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] conducted in a 125 L Batequip flotation cell. Understanding solids suspension has become increasingly important due to dramatic increases in flotation cell sizes. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension. The minerals used in this study were apatite, quartz and hematite. The critical impeller speed was found to be strongly dependent on particle size, solids density and air flow rate, with solids concentration having a lesser influence. Liquid viscosity was found to have a negligible effect. The general Zwietering-type critical impeller speed correlation developed by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621–629] was found to be applicable to all three flotation machines. The exponents for particle size, solids concentration and liquid viscosity were equivalent for all three cells. The exponent for solids density was found to be less significant than that obtained by the previous authors, and to be consistent with values reported in the general literature for stirred tanks. Finally, a new dimensionless critical impeller speed correlation is proposed where the particle size is divided by the impeller diameter. This modified equation generally predicts the experimental measurements well, with most predictions within 10% of the experimental.     

Maximum size of floating particles in different flotation cells

Two flotation models, particle at the liquid-gas interface and particle-bubble aggregate, both based on balance of forces, were used for evaluation of experimental data relating the maximum size of floating particles d_max and their advancing contact angle. It was noticed, by comparing the experimental and model data, that for a given flotation device and material the maximum size of floating particle d_max increases with increasing particle hydrophobicity and at the same time the acceleration a, experienced by the d_max particle at the moment of rupture, decreases with particle hydrophobicity. The acceleration values change with cell dynamics and type of flotation device and are usually not available, therefore empirical apparent cell constants A, which characterize flotation dynamics and relate particle acceleration with advancing contact angle have been proposed instead. The values of A were determined by evaluation of experimental data relating d_max and advancing (detachment) contact angle for constant: particle density, medium density, surface tension, and flotation cell dynamics. Since A depends on particle density, a tentative formula was proposed to link A with density-independent flotation cell constant A_o. The values of A_o for selected flotation cells were calculated and presented.Using quartz as an example, it was shown in the paper that a positive advancing contact angle does not guarantee flotation because a prerequisite for flotation is non-zero receding contact angle.     

促进剂对煤泥浮选速度的影响研究

以天然油脂棉籽油和工业副产品为主要原料,合成出脂肪酸单甘油酯硫酸盐PGS,将之作为浮选促进剂(3%),与柴油(27%)、水(70%)制备出新型煤用乳化浮选捕收剂ZFC。分别以ZFC和柴油作为捕收剂,对两种1/3焦煤进行浮选速度试验,并应用一级浮选动力学方程进行拟合,得到两种煤样的动力学方程,通过对比得出:以ZFC做捕收剂,所用煤样的浮选速率常数和浮选速度均优于柴油。对PGS促进剂作用前后煤样的疏水性、红外光谱、润湿热进行检测,结果表明:PGS促进剂和煤粒表面发生化学吸附,促进剂的疏水性基团朝外,因此提高了煤粒表面的疏水性;乳化药剂和煤粒的吸附强度及稳定性显著提高,煤粒在随气泡上升过程中不易脱落,从而提高了浮选速度。     

小规模鳞片石墨矿浮选工艺研究

本文通过试验发现：山东某小规模鳞片石墨矿可以采用采用一段粗磨,粗精矿经过三段再磨,四次精选的选矿工艺,获得品位达到90.43%的鳞片石墨精矿。该工艺流程简单,大片产率高,生产的精矿品位符合中碳石墨要求,从而为开发利用山东东部零散存在的鳞片石墨矿资源提供了技术可行性。     

Effect of particle size on flotation performance of complex sulphide ores

Flotation processes occurring in the bulk and froth phases have a characteristic influence on the structural features and dynamics of the flotation froth. It is recognized that the structure and texture of a mineral froth is a good indicator of flotation separation performance. The surface froth feature and dynamics are presented by three features extracted from the digitized images of the froths, i.e. SNE, a rough indication of the average bubble size of the froth, froth stability and the average grey level of the froth, an indication of mineral loading. Particle size is an important parameter in flotation operation. Nowadays, particle size is often measured and controlled in flotation concentrators. In this study the dependence of the froth structures on the particle size variation was investigated on the batch flotation of a sulfide ore from the Merensky reef in South Africa, and the size by size recovery curves were studied as well. In general medium particles produced bubbles smaller than those observed in the presence of fine and coarse particles, and the recovery rates were larger. Entrainment was a contributory mechanism to the recovery of fine particles. The fluctuation of flotation indices on the particle size change can be diagnosed and predicted by the froth structures change with a high degree of accuracy.     

Methodologies for the evaluation of grinding media consumption rates at full plant scale

Due recognition of the significant impact of the cost of grinding media on the overall economics of comminution facilities worldwide has created the need for reliable, practical methodologies to compare—over extended control periods—different operating conditions, arising from eventual changes in ore type, ball supplier or simply, a trial of new products from the same supplier. The current publication describes the main aspects to be considered in the planning and execution of a full scale evaluation campaign, the actual data to be recorded and the required calculation routines, including the theoretical framework justifying their applicability.The Linear Wear Model, herein described, provides a theoretical framework for the best estimations of comparative grinding media wear performance (in the absence of ball breakage) in any given application, on the basis of the Specific Wear Rate Constant, (μm/(kW h/ton)), derived from the Specific Consumption Rate (gr/kW h), corrected by actual make-up ball size (mm). When significant ball breakage is to be expected—as in semiautogenous grinding (SAG) applications—an expanded, conceptual model, based on pilot Drop Ball Testing (DBT) results is gaining acceptance as a way to incorporate breakage as a possible media consumption mechanism.Ideally, evaluations should be conducted in parallel grinding sections, in order to have the option of establishing multiple sequential, concurrent or cross-reference comparisons. The evaluation period should cover at least 6 months after the complete ‘purge’ of the string of balls being substituted, which may well take from 3 to 6 months. As a result, the evaluation period required for reliable conclusions should typically exceed 9–12 months of fairly undisrupted, normal operation.The methodologies here proposed make intensive use of Moly-Cop Tools, a software package developed by the international Moly-Cop Grinding Systems organization (formerly, ARMCO Worldwide Grinding Systems) with the specific purpose of helping process engineers characterize and evaluate the operating efficiency of any given grinding circuit, following standardized methodologies and widely accepted evaluation criteria.     

转速对铝铜FSW接头组织与性能影响

采用搅拌摩擦焊设备对3mm厚6082铝合金和T2紫铜进行连接,通过金相显微镜、硬度测试、拉伸实验等,探究转速对焊接接头组织与力学性能影响。结果表明：焊接转速为1000 r/min,焊接速度为50 mm/min,偏移量为0.6 mm,焊缝成形效果最佳,Al/Cu相互嵌入,呈现钩子形态,焊核区出现明显的金属塑性流线,生成Al4Cu9、AlCu、Al2Cu、Al2Cu3金属间化合物;焊核区显微硬度波动大,峰值出现于界面位置,这是由于该处生成Al-Cu金属间化合物造成的;随着转速的增加,抗拉强度先增大后减小,最大抗拉强度可达255 MPa,为Al母材抗拉强度的82%,断裂位置位于铝铜结合处,呈韧性断裂。     

A model to relate the flotation rate constant and the bubble surface area flux in mechanical flotation cells

Two recent flotation models developed by the authors are discussed, viz. the bubble population balance model and the attachment-detachment model. The bubble population balance model describes the history of a bubble population in a flotation cell in terms of the sub-processes of bubble breakage and coalescence. The attachment-detachment model allows for the presence of a gas phase in the flotation cell, both in terms of a gas residence time and the attachment and detachment of mineral particles to/from bubbles. When combined the two models predict a near-linear region about a point of inflexion on the (simulated) response between the flotation rate constant (k) and the flux of bubble surface area through the flotation cell (S_b). It is proposed by the authors that this region corresponds to the linear k−S_b relationship observed in a recent research project on flotation kinetics in mechanical flotation cells by Gorain et al. (1997).     

Effect of speed and accuracy of on-line elemental analysis on flotation control performance

In this paper the control performance of the flotation process is evaluated as a function of the measurement accuracy and sampling frequency of an on-stream analyzer. First, the performance of rule-based control and model predictive control (MPC) strategies is studied using discrete flotation models and the respective performance indices. Next, the net smelter return (NSR) is calculated for varying sampling rate and accuracy combinations using the PI controllers-based control strategy, mechanistic flotation models and the industrial process data as input. The control and economical performance of the process declines strongly when the sampling cycle is increased. The results also indicate that the speed of on-line analysis has a significant effect on the production economics, calculated as the average net smelter return.