Laboratory Grinding Research Articles

Industrial versus Laboratory Clinker Processing Using Grinding Aids (Scale Effect)

The evaluation of grinding aid (GA) effect on clinker processing in laboratory grinding mills is relatively simple. Yet, the results obtained cannot be directly transposed to industrial mills, given the fundamentally different operational modes and grinding parameters. This paper seeks to evaluate the scale effect by comparing the results obtained from a closed-circuit tube mill operating at 90 ton/hr to those determined using a 50-liter laboratory mill. Tests results have shown that the decrease in specific energy consumption (Ec) due to glycol or amine-based GA can be evaluated under laboratory conditions. However, such tests underestimate the actual performance that could be achieved in real-scale mills; the Ec reduction due to GA is around twofold higher when grinding is performed in real-scale mill. Compared to industrial tests, the cement particle size distribution curves widened and shifted towards higher diameters when grinding was performed under laboratory conditions, particularly with GA additions. This led to remarkable changes in water demand, setting time, and 1- and 28-day compressive strengths.

Technological requirements of the new copper smelter of RTB Bor: A great challenge for the mining profession and science

The research results show the possibility of improvement the basic technological parameters of copper flotation in the copper mine Majdanpek. With increasing the fineness of definite grinding product from 55 % to 65 % of grain size class -74 μm, as well as optimizing the pH value of the pulp, the type and dose of collectors and frothers, there was an increase of copper recovery for 9.35% and the quality of primary concentrate for 0.54 % or about 40 %. The compared technological parameters of the industrial process of flotation, in the laboratory experiment with optimal parameters is achieved an increase of the copper recovery for 7.56 % and concentrate quality for 0.61%, or about 50%. The analysis of the achieved technological parameters on narrow grain size classes of grinding products in industrial and laboratory tests, show unfavorable granulometric composition, both in terms of low participation of optimal floating class (-74+37) μm 15.75 % and a relatively large share of classes, + 147 μm and - 37 μm, which achieve much worse technological indicators in the process of basic flotation. The great similarity of granulometric composition of the industrial grinding product, which works in a closed circuit of grinding and sizing, and discontinuous, laboratory grinding, indicates the lack of efficiency of industrial process. The consequences of ineffective grinding, improper values of circulative charge and decreased sharpness of classification in a closed cycle of grinding and classification, are overgrinding of material, i.e. the increased participation of the finest and coarsest class of definite grinding product, or worse technological parameters, copper recovery and concentrate quality in the basic flotation process.

Simulation of a ball mill operating with a low ball charge level and a balanced ball size distribution

The optimization of industrial grinding circuits has been successfully performed using mathematical models that describe the industrial scale data from breakage parameters determined in laboratory grinding tests. The test material studied here is a gold ore ground in a closed ball mill circuit with hydrocyclone classification. Several sampling campaigns were carried out aiming to produce mass balances and provide material for laboratory tests. The parameters determined in the laboratory tests were used to predict, by simulation, the circuit behavior with a low ball charge level and a balanced ball size distribution.

Post-hot isostatic pressing: A healing treatment for process related defects and laboratory grinding damage of dental zirconia?

ObjectiveProcessing parameters (powder granulation, compaction, debinding, greenbody shaping, sintering) and post-sinter rough, even fine grinding are influencing the final mechanical properties of 3Y-TZP. The hypothesis of this study was that post-sinter hot isostatic pressing (post-HIP) would be beneficial for improving reliability and strength of both sintered and coarse ground sintered zirconia by closing or reducing surface and/or small volume defects. Methods75 sintered bars of an experimental 3Y-TZP (3mm×4mm×45mm) with chamfered edges and 15μm diamond surface finish were provided by the manufacturer (Ivoclar Vivadent) and randomly distributed in five groups of N=15 each. G1 served as control (as received); G2 was post-HIPed at 1400°C and G3 at 1350°C, both using a pressure of 195MPa in Ar for 1h; G4 was coarse ground with 120μm diamond disk grain size; G5 was ground 120μm and post-HIPed at 1350°C at 195MPa, 1h in Ar. The specimens were fractured in air in 4 point-bending. Weibull characteristic strength (σ0) in MPa, m parameter (reliability) and confidence intervals (CI) at 90% confidence level are reported. Identification of the critical flaw was performed by SEM on the fractured surface of all specimens and XRD performed in all groups. ResultsG1: σ0=973 (932–1016), m=10.6 (7.45–15.1); G2: σ0=930 (871–995), m=6.9 (4.87–9.9); G3: σ0=898 (848–952), m=7.94 (5.6–11.4); G4: σ0=921 (857–991), m=6.35 (4.48–9.11); G5: σ0=881 (847–918), m=11.4 (8.03–16.3). G5 had a significantly lower σ0 than G1. No significant differences were seen in the reliability (m) among the groups. Fractography revealed critical intrinsic subsurface flaws of 10–60μm present in all groups resulting from the processing parameters. No “healing” (i.e. closing of defects by densification) resulted after post-HIP. Grinding sintered zirconia with 120μm diamond disks induced radial cracks of 10–20μm and an important pseudo-cubic phase transformation (56wt%) that was not completely removed after post-HIP. Post-HIP increased slightly the relative density by 0.1% but without improving the strength and reliability. SignificancePost-HIP was not efficient in closing large (10–60μm) subsurface (volume) processing defects.

Influence of Selected Grinding Specifications on the Fly Ash Granulometry

A variety of fine grained alternative materials are used in concrete composition, mainly as SCMs (Supplementary Cementitious Materials). Although the utilization of alternative materials in its natural form is preferred on account of energy saving, the global development of consumer society tends to enormous growing of wastes and to problems with disposal. That is why the necessity of their utilization, even at cost of higher processing, is mentioned increasingly. The rate of some wastes valorization can be improved in this way together with the benefit of better/new concrete parameters.Results of fineness treatment of fly ash for specific properties and utilization of concrete is presented in the paper. The commercial grinding in ball mill, as well as laboratory grinding in planetary ball mill, were practiced, while the variables were both, the grinding time (30, 45 and 60minutes, and 18, 30, 42 and 60minutes respectively) and application of grinding aids. The granulometry of samples was determined using the laser granulometer and analyzed in the terms of possible gain the extremely fine particles.

Development of Size Reduction Equations for Calculating Energy Input for Grinding Lignocellulosic Particles

Size reduction is an essential and often first operation in preparing biomass for subsequent operations. Size reduction is energy intensive especially for cases where the target particle is small and precise in dimension. Mineral and food industries have developed empirical and semi-empirical equations to calculate energy input for grinding. It is uncertain if these equations can be applied to fibrous biomass. This research presents laboratory grinding data to evaluate the applicability of a set of generalized industrial-size reduction equations to the grinding of lignocellulose biomass. Batches of Douglas-fir (a soft wood) and hybrid willow (a hard wood) particles conditioned to 11.5% moisture content were ground in a rotary knife mill. Input and output particle sizes and the level of energy used to grind the material were acquired electronically and recorded. Specific grinding energy (J/g) was correlated with size parameters of three popular industrial equations: Kick, Rittinger, and Bond. All three equations fitted to the experimental data linearly but the best fitted lines did not go through the origin, i.e. the fitted lines had a slope and intercept. Rittinger equation had the best fit, followed by Bond equation and Kick equation.

Effect of feed preparation on copper activation in flotation of Mt Keith pentlandite

In this work, the effect of copper sulphate on the flotation of Mt Keith pentlandite ores was studied. As Mt Keith operates separate size flotation circuits, e.g. slime (−8 μm), fine (−25 μm) and coarse (−160 μm) circuits, tests were conducted on streams of different particle size distributions prepared with the use of cyclones. The flotation response with and without the addition of copper sulphate was examined, first, on feed streams prepared by a laboratory grinding mill and cyclone and, second, on streams collected directly from the plant. It was found that copper sulphate had an adverse effect on flotation performance when the flotation feeds were prepared in the laboratory. In the flotation of slime-fine fractions that combined slime and fine particles, the addition of copper sulphate depressed nickel flotation while increasing gangue entrainment. In the flotation of coarse fractions, the addition of copper sulphate depressed nickel flotation without affecting gangue entrainment. However, when samples were collected directly from the plant streams and floated in a laboratory flotation cell, the addition of copper sulphate increased nickel recovery without affecting gangue entrainment in the flotation of slime, fine and coarse fractions. To explain this discrepancy, pulp chemistries in the two different types of tests were compared. It was found that the plant mills at Mt Keith produced a much more reducing grinding environment than the laboratory mill. This might contribute to the completely different behaviour which copper sulphate exhibited on flotation performance. This study also demonstrates the importance in considering plant pulp chemistry during research development in a laboratory.

Ethnobotanical Identification and Anti-microbial Evaluation of Some Anti-Diarrhoeal Plants Used by the Samburu Community, Kenya

Aims: The antibacterial effect of some selected Samburu medicinal plants were evaluated on bacterial strains like Staphylococcus aureus-ATCC 20591, Bacillus subtillis-local isolate, Salmonella typhi-ATCC 2202, Escherichia coli-STD� 25922 and Pseudomonas aeruginosaATCC 25852. Methodology and Results: Methanol was used as an extraction solvent for the medicinal plants after they had been dried and ground using the laboratory grinding miller. The in vitro antibacterial activity was performed by agar disc diffusion method. The significant antimicrobial ac tivity of active extracts was compared with the standard antibiotics, cefrodoxima and amoxicillin. These results were significant at p < 0.01. The MICs were also determined by the micro titreplate method. The MICs of the most active pla nts ranged from 18.75 mg/mL to 37.5 mg/mL. The MBCs ranged between 18.75 mg/mL to 37.5 mg/mL. The most active plant that had substantial activity in at least all the test cultures was found to be Lannea triphylla (A.Rich) Engl. A number of phytochemicals were also found to be present with tannins being the most abundant followed by flavonoids and saponins. Conclusion, significance and impact of study: The findings show that most of the medicinal plants used by the Samburu community have some significant activity on the bacterial isolates known to cause diarrhoea.

Fine-dispersed and nano mineral particles in mining and metallurgical wastes after commercial and laboratory grinding

The paper presents the results of defining the content of fine-grained fractions and nanofractions in mining wastes and the correlation equations for express estimate of powder dispensability. The authors discuss the non-uniqueness of the “fine-grained mineral particles and nanoparticles” notions in scientific literature.

Alteration in amorphicity of quartz structures during grinding of ferrous quartzites

The author discusses evaluation of coherent-scattering regions in quartz in the structure of ferrous quartzites during commercial and laboratory grinding of wet magnetic separation refuses and the correlation equation that confirms the activity versus dispersion behavior of the analyzed refuses.

Modeling and optimization of high chromium alloy wear in phosphate laboratory grinding mill with fuzzy logic and particle swarm optimization technique

This study evaluated the potential of fuzzy logic as an alternative method to the traditional statistical regression techniques, which were employed in a previous publication ( Chen et al., 2006), for predicting the wear rate of high chromium alloy during phosphate grinding. Moreover an attempt has been made to use a novel particle swarm optimization technique to determine the optimum process parameters for minimum wear rate. The comparison of a fuzzy model and a regression model, which was assessed by various measures (i.e., root mean square error (RMSE), R 2 and the percentage of predicted values that are within the 5% tolerance of the corresponding actual values), showed the superiority of the developed fuzzy model. The optimization results indicated that the minimum liner wear rate can be obtained with solution pH of 10.5, a rotation speed of 52 rpm, a solid concentration of 63% and a crop load 70%.

The effect of ore blends on the mineral processing of platinum ores

This paper investigates whether blends of platinum ores display linear grinding and flotation characteristics or whether non-linear effects occur, i.e. synergistic/antagonistic effects. Ores from four different shafts are used in the study, i.e. Salene, Waterval UG2, Paardekraal and Townlands. Laboratory grinding and flotation tests are conducted on blends of the four ores using a statistical simplex lattice mixture design. Grinding results show no evidence that blends of ores display non-linear grinding characteristics. Flotation results show significant antagonistic effects in binary blends of the Salene ore with the other ore types. On the other hand, ternary/quaternary blends of ores result in synergistic effects. The study concludes that blends of platinum ores display non-linear (non-additive) characteristics when there are large differences in metallurgical properties between the ore types. The study demonstrates that appropriately designed mixtures experiments are an effective way to study the performance of ore blends in the laboratory.

Should the slurry density in a grinding mill be adjusted as a function of grinding media size?

The slurry density or pulp percentage of solids and the size of the grinding media are often considered for ball mill optimization. Laboratory grinding tests were conducted to identify possible interactions between the two variables and the fineness of the ground product. Preliminary results show that there is no need to adjust mill slurry density when adjusting the size of the grinding media in a ball mill.

A comparative study on damage detection in speed-up and coast-down process of grinding spindle-typed rotor-bearing system

Abstract In this paper, the damage detection from non-stationary mechanical vibration signals collected during acceleration and deceleration was performed. A laboratory grinding spindle-typed rotor-bearing system was equipped, and modal testing was carried out to identify system characteristics and operating range. Time–frequency analysis method such as Fast Fourier Transform (FFT), Short-Time Fourier Transform (STFT), Wigner–Ville Distribution (WVD), and Discrete Wavelet Transform (DWT) was applied to vibration data of normal rotor and shaft-cracked rotor in speed-varying process and the results of feature extraction from shaft-cracked condition were also compared with those in normal condition.

GRINDING PROCESS SIMULATION BASED ON ROSIN-RAMMLER EQUATION

In many grinding cases, mainly during the last stages of the process, the cumulative particle size distribution is found to follow the Rosin-Rammler equation (RR), the parameters of which can be used as essential criteria to the operation progress. This article presents a method for developing a simplified, easy-to-use process model by utilizing data from laboratory grinding of limestone and clinker and applying some appropriate mathematical transformations to the RR. The proposed simulation model follows the evolution of the particle size range below 200 µm and allows for adequate precision during the last, most energy-consuming grinding stages. These process stages are also the most decisive in defining the final product size distribution profile. By applying the model, in laboratory and industrial scale, it is possible to combine the characteristics of the materials of interest and the grinding equipment with the RR parameters, the latter expressed as process-time or energy consumption functions.

A microscale look at tumbling mill scale-up using high fidelity simulation

Tumbling mill scale-up has had largely empirical roots. Energy size and energy size distribution relationships have been derived from relatively large data bases combined with a sprinkling of fundamental science. High fidelity simulation (HFS), which is based on multi-physics models, allows one to examine the interactions that occur in a mill amongst media, particles, wear parts and slurry at the microscale level. Thus, fundamental questions concerning particle capture, energy utilization and fragment creation as they depend on “equipment size” can be addressed. In this paper, the process is taken from the single particle breakage level, through laboratory grinding experiments up to full-scale commercial mill operation. The basis for certain empirical relationships is explained in fundamental terms. A look at the future of scale-up based on the use of such tools is presented.

A graphical method to assess size reduction by grinding

A graphical method to assess the size reduction by grinding is presented and illustrated with data collected from laboratory grinding tests and industrial grinding circuits. The method lies between the graphical comparison of size distributions and the population balance model. The method is easy to apply and provides a quick way to compare grinding mill performances under various operating conditions and processed ores. The application of the method to industrial mills shows that a grinding mill operation could present an invariant behaviour that can be exploited for simulation purposes.

The Magotteaux Mill ®: investigating the effect of grinding media on pulp chemistry and flotation performance

Many laboratory studies are completed each year exploring the flotation response of old and new ore sources. Most pay little attention to the impact grinding media has on down stream processing or even attempt to match the laboratory grinding chemistry to comparable plant data. The Magotteaux Mill ®, described in this paper, allows the user to measure, monitor and control the pulp chemical conditions during grinding. This ultimately means that it is now possible to prepare ore samples in the laboratory that have the same properties as those in the plant (i.e. particle size distribution and pulp chemistry).

New Laboratory Grinding Equipment

Equipment intended for laboratory and semi-industrial application makes it possible to crush components, in order to obtain batches with prescribed fractions sizes, mix the components, implement their mechanical activation, etc.

Effect of grinding media and NaHS on copper recovery at Northparkes Mines

The flotation behaviour of copper minerals in the Northparkes Mines copper-gold ore is dependent on grinding media (and hence grinding Eh) and aeration during conditioning. Laboratory grinding and flotation tests were conducted using mild steel and stainless steel rods with and without the addition of sodium hydrosulphide (NaHS) in the conditioning stage. In the absence of NaHS, grinding using stainless steel media increased the kinetics of subsequent copper mineral flotation compared to the use of mild steel media. Flotation kinetics after grinding using mild steel media were increased by aeration prior to reagent addition. The addition of NaHS after grinding using mild steel rods increased the froth stability by increasing froth mineralisation, thus increasing the flotation kinetics of the copper minerals. When stainless steel grinding media was used, the copper flotation recovery was very high (>90 % in the rougher stage) without the addition of NaHS, so its use was not warranted. The flotation of the bornite was not reduced by oxidation, in fact copper mineral recovery was the highest under the most oxidising grinding conditions.