Bond Work Index Research Articles

Grain-size distribution of starting sample of size class -3.35 mm: Reliability factor of the Bond work index of grindability

The investigation of the Bond' work index of grindability of low-grade and high-grade copper ore from the Copper Mine Bor has given two, for the theory and practice of comminution processes, significant results. The first confirms the previous theoretical and practical experiences on these raw materials, which is slightly higher fragmentation resistance of low-grade copper ore, compared to high-grade copper ore Wi p=14.11 kWh/t and Wi rs=13.35 kWh/t, respectively. The second result indicates the effect of grain-size distribution of starting sample, size class -3.35 mm, for determination the Bond' work index -3.35 mm size class, on the values of Bond work index, Wi r=14.11 kWh/t and Wi rs=13.35 kWh/t. The slight difference in resistance to fragmentation of tested copper ore samples gave the possibility of common processing of these raw materials. The stated effect of grain-size distribution of starting sample on the value of Bond work index, has a theoretical as well as a practical significance in designing and selection of process equipment in the grinding process. The grinding kinetics of low-grade and highgrade copper ore, as well as different times, required to obtain the grinding products of certain fineness confirm the previous statement.

Dependence of the Bond work index of grindability on grain-size distribution of the starting sample of size class -3.35mm

The research results of the effect of grain-size distribution of the starting sample of size class -3.35 mm on the value of the Bond work index OF grindability, obtained by the method of shortened procedure by prof. N. Magdalinović, clearly indicate that the characteristics of starting sample significantly affects the value of resistance to comminution. Differences in values of the Bond work index of grindability for low-grade copper ore of 5.4 kWh/t or about 42 % and high-grade copper ore of 3.77 kWh/t or about 35%, from the point of the theory of comminution and practical application in designing and selection of process equipment are of particular importance.

Grindability of binary ore blends in ball mills

The understanding of how blends of materials grind is of great relevance in both the minerals and the cement industries. If benefits and challenges associated to it are properly understood, then decisions can be made on blending prior to grinding or grinding additives in separate during cement production, as well as different ores fed to mills in a processing plant. The paper investigates the size reduction of blends of materials with different grindabilities in a Bond ball mill, as well as in a continuous pilot-scale mill. The accumulation of the harder (tougher) component in the mill charge as grinding progresses is analyzed and a simple empirical model that describes this phenomenon has been proposed. It is found that the accumulation of hard component in the mill increases with the decrease in the ratio of Bond work index values of the individual soft and hard components, and with the increase in the circulating load ratio. It is also concluded that the Bond work index of the mixtures is often higher than the weighed-average value of the individual components in the mixture. As such, an expression is proposed for calculating the value for blends based on this modeled accumulation effect and has been found to remove the bias from predictions made on the basis of the weighed-average values from the feed.

Rapid determination of Bond rod-mill work index by modeling the grinding kinetics

Generally, Bond work index is a common method for selecting comminution equipment as well as estimation of grinding efficiency and calculating required power. In the current research, a simple, fast and accurate procedure is introduced to find the rod-mill work index based on the conventional Bond work index. The grinding experiments were carried out on four typical samples of iron, copper, manganese and lead–zinc ore with three test-sieves in specified time periods and aimed to shortening the procedure. Furthermore, the grinding kinetics and mass balance equations were applied to model the standard Bond rod-mill work index. For comparing the standard Bond rod-mill work index and the new modeled method, work index (Wi) and produced fine particles in a cycle (Gi) for the four samples determined. The performed paired Student’s t-test results indicated that the Standard Deviation for Gi and Wi obtained by the shortened method are respectively 0.50 and 0.58 in respect of traditional Bond method.

Determination of the Bond work index on samples of non-standard size

The Bond work index, Wi, is defined in a Bond ball mill on the samples of standard size −3.327+0mm. In practice, it is possible to find materials of non-standard size that are finer than 3.327mm.In this work, a procedure for the calculation of the Bond work index is suggested for cases when the Bond grindability test is conducted on samples of non-standard size.

Grindability determination of torrefied biomass materials using the Hybrid Work Index

The grindability of torrefied biomass materials is a difficult parameter to evaluate due to its inhomogeneous character and non-uniform morphology. However, it is necessary to develop a grinding test that is representative of the wide ranging character of biomass and torrefied biomass materials. Previous research has shown that Resistance to Impact Milling (RIM) can be linearly correlated to thermally driven weight loss in biomass. In particular, the RIM equipment was found to supply the right energy level to physically break down structurally deficient biomass materials while leaving the un-touched material relatively intact [1–3]. However, the RIM procedure was not designed to extract the comminution energy. Alternatively, the Bond Work Index (BWI) procedure was developed to accurately assess the grinding energy of brittle materials [4,5]. However, the milling energy is too low to be effective for biomass comminution. In this research, the BWI procedure was utilized with the ball–mill approach in the RIM test to evaluate torrefied biomass materials. The hybridized procedure has been shown to be both highly correlated to energy consumption and sensitive to degree of torrefaction. The proposed Hybrid Work Index (HWI) is certainly useful for assessing torrefaction in a laboratory environment, but it may also be correlated to grinding energy at industrial scales.

Effects of ore characteristics on product shape properties and breakage mechanisms in industrial SAG mills

The effect of ore characteristics on the particle shape were studied using two detailed industrial surveys to monitor breakage events taking place inside industrial Semi-Autogenous (SAG) mills as a function of ore hardness. In order to validate the ore hardness effect, the SAG mill was operated in a controlled condition as much as possible. Different methods, including point load index, drop weight test, Bond mill work index and abrasion index, were employed to appropriately characterize the entering feed strength to the circuit. In addition, the shape of SAG mill products was quantified using an image analyzer system, for which elongation and angularity descriptors were calculated.Experimental studies have indicated that an increase in ore hardness is associated with an increase in point load index and Bond work index and a decrease in impact breakage parameter (A×b). Moreover, an increase in ore hardness corresponds to an increase in feed size. Hard ore grinding in the SAG mill resulted in finer products compared to the soft ore milling. In addition, it was found that the products of the soft ore milling were more elongated, angular and less rounded than those of the hard ore milling. This was attributed to changes in breakage mechanisms as ore strength changes. The weaker ore is ground mainly by the impact breakage while the stronger ore is subjected to abrasion and attrition events where the media impact could not sufficiently break the stronger particles. It was also found that the particle angularity and elongation distributions were fitted to the 3-parameter lognormal distribution, providing a convenient way to quantify changes in particle shape properties as a function of the ore characteristics. It was concluded that the main reason underlying the decrease of circuit throughput from 939 to 498t/h was due to changes in breakage mechanisms.

A correlation between Vickers Hardness indentation values and the Bond Work Index for the grinding of brittle minerals

Comminution of materials is an energy intensive and inefficient process where predetermination of energy consumption for the production of a mineral powder may require lengthy and costly testing. This investigation was conducted to asses an unanticipated correlation between Vickers Hardness (VH) values for crystalline minerals and their comminution energy requirements as expressed by the Bond Work Index (BWI).Based on preliminary investigations, hardness values of crystalline minerals as measured by the VH test are interpreted to be affected by their elasticity. A tentative mathematical relation with a high correlation between the VH of liberated, mono-crystalline minerals and their BWI is presented. This relation probably predicts the maximum comminution energy requirements as mineral products for grinding are usually constituted by particles relatively free of extraneous planes of weakness.The VH test is proposed as a potential, rapid alternative method for determination of BWI values for the grinding of minerals. It may also potentially assist in the assessment of energy losses due to excessive grinding of mineral ores.

Correlation Between Work Index and Mechanical Properties of some Saudi Ores

Abstract The crushing energy for applications in the mineral processing industry is usually determined by an empirical bond index, regardless of the mechanical properties of a rock. Although several attempts have been made to obtain the comminution energy based on theoretical approaches, it would be beneficial to examine this relation based on a physical concept. In this paper, some Saudi samples of bauxite, kaolinite, granodiorite, magnetite, granite, feldspar and quartz were tested for hardness, abrasion, compressive strength as well as modulus of elasticity and the bond work index of these samples was estimated. The value of the bond work index of the above samples has shown a variation from 10.8 kWh ton-1 for bauxite (high abrasion value and low compressive strength) to 20.4 kWh ton-1 for granite (low abrasion value and high modulus of elasticity). The correlation between the abrasion value (X2) and work index (Wi) is found to be Wi = −1.8 Ln(X2) + 11.5 with a correlation coefficient of 0.80.

Lithotamnian limestone from the deposit 'Dobrilovici' in flue gas desulphurization by wet process

This paper presents the results of investigation lithotamnian limestone from the 'Dobrilovici' deposit for the use in flue gas desulphurization by wet process. According to the technological process conditions, FGD limestone should fulfill the certain criteria in order to be used for that purpose. In respect to those criteria, this paper investigates the chemical composition, bulk density, grain-size distribution and Bond work index (kWh/t). The results of these investigations have showed that limestone from 'Dobrilovici' deposits, according to its physicochemical properties, is completely suitable for the flue gas desulphurization process in thermal power plants, as well as for disposable gypsum obtaining.

CORRELATION BETWEEN BOND WORK INDEX AND MECHANICAL PROPERTIES OF SOME SAUDI ORES

The crushing energy in mineral processing industry is usually determined by empirical Bond index, regardless of the mechanical properties of a rock. Although several attempts have been made to obtain the comminution energy based on theoretical approaches, it would be beneficial to examine this relation based on physical concept. In this paper, some Saudi samples of bauxite, kaolinite, granodiorite, magnetite, granite, feldspar and quartz were tested for hardness, abrasion, compressive strength and modulus of elasticity and the bond work index of these samples were estimated. The value of Bond work index of the above samples has shown a variation from 10.8 kwh ton-1 for bauxite (high abrasion value and low compressive strength) to 20.4 kwh ton-1 for granite (low abrasion value and high modulus of elasticity). The correlation between the abrasion value(X2) and work index (Wi) is found to be Wi = -1.8 Ln (X2) + 11.5 with correlation coefficient of 0.80.

Grindability characteristics of lateritic and karst bauxites

The Bayer process is the most frequently used method for the production of alumina from bauxite worldwide. The aim of the process is to grind and dissolve the alumina-rich minerals into hot caustic solution, than to separate the insoluble phases. These are followed by precipitation and calcination to produce alumina (Al 2O 3). After the crushing step the bauxite has to be ground usually in spent liquor at 60…100 °C in a tumbling ball mill for dissolution. Due to the above special circumstances the determination of the specific grinding energy or the Bond work index for designing new grinding facilities and the optimization of the existing operations (grinding ball charge, filling ratio, revolution number, operating of classifier, etc.…) was not reliable when the traditional laboratory mills (Hardgrove-, Bond-, Zeisel mill) and procedures were used. To meet the requirements based on the standard grindability tests suitable methods and apparatuses were developed at the Institute of Raw Material Preparation and Environmental Process Engineering, University of Miskolc, called Universal Hardgrove- and Bond mill. This paper presents briefly these laboratory apparatuses and methods and shows the most important results of the systematic research work carried out recently concerning the grindability of lateritic and karst bauxites. Parallel experiments were performed using the Universal Hardgrove- and Bond mill and the measurement data were compared. The samples originated from three continents worldwide: Africa (Boké), Australia (Weipa) and Europe (Greece and Hungary). The results show good correlation between the developed methods. Temperature and caustic media are very important affecting parameters to the Bond work index, which can be demonstrated by the above mentioned developed laboratory mills and methods.

Analysis of energy–size reduction relationships in batch tumbling ball mills

A theoretical energy–size reduction relationship is derived for tumbling ball mills based on a solution of the integro-differential equation of comminution kinetics, in which the proportional relationship is applied between the grinding rate constant and the net mill power. The derived formula is similar to an empirical energy law, d W ∝ d x r / x r i , where W is the specific energy input, x r is the particle size of product and the exponent i is shown to be a variable depending upon the ground material, the type of mill and the method to measure energy. Derived results are confirmed with reported data in reasonable agreement. Also, the Bond's energy law is examined and a method for the correction of the Bond work index is discussed.

A new size distribution model by t-family curves for comminution of limestones in an impact crusher

In the evaluation of crushers, t-family curves obtained from single particle test methods are frequently used. It is known that there are many difficulties and problems in these tests. In this study the breakage behaviour of three different limestones in an impact crusher was investigated. A new size distribution model was developed by t-family value evaluation and Bond work index approach. As a result, the validity of the equation was proved by a high regression value ( r 2 = 0.88).

Physical, gravimetric and functional characterization of various milling fractions of popped gorgon nut (Euryale ferox)

Studies were carried out on the milling characteristics to increase the usability of popped gorgon nut (makhana). It was conditioned to 6.2, 9.4 and 12.3% (db) moisture content and ground in a hammer mill at feed rates of 3, 6 and 9kg/h. The differential screen analysis showed that increase in moisture content decreased the percent weight retained in the pan and produced more medium sized particles (0.592-0.157mm). The Bond's work index, Kick's constant and average particle size increased but total surface area decreased with the increase of conditioning level. However, feed rate showed the antagonistic effect on these parameters. Various grinding characteristics were significantly affected either individually or in combination (interaction) by the conditioning level as well as the feed rate and could be well correlated in terms of Bond's work index, Kick's constant, total surface area, average particle size, effectiveness of milling and bulk density for popped makhana.

Comparison of the overall circuit performance in the cement industry: High compression milling vs. ball milling technology

In cement production, tube mills having multi-chambers are traditionally used either in open or closed circuit operations. After the introduction of high compression grinding mills (High pressure grinding rolls (HPGR), vertical roller mill (VRM) and Horomill), various circuit configurations have been developed for energy efficient grinding. In this study, in order to evaluate and compare the performances of these cement grinding technologies, industrial scale data were collected from HPGR-ball mill, VRM, Horomill and multi-chamber ball mill closed circuits. The grind abilities of the raw materials of all circuits were varying in a narrow range of 14–20 kWh/t. The specific energy consumptions of the grinding equipment and the standard bond work indexes, used 100 μm screen, of raw materials are given below. Circuit Bond work index (kWh/t) Specific energy consumption (kWh/t) HPGR-ball mill 14.7 20.0 VRM 19.6 27.5 Horomill 14.4 17.5 Ball mill 14.4 32.5 The results show that high compression grinding mill circuits are more energy efficient than conventional single stage multi-chamber ball mill circuits. The circulating load ratio around the circuit is much higher compared to conventional ball milling. The reason is less fine and slime production of the high compression technology which prevents the over-grinding.

Determination of Bond index of Birnin- Gwari Iron Ore in Nigeria

Bond index is useful in designing of grinding system in mineral processing. In this study, the Bond work index of Birnin- Gwari iron ore in northern Nigeria is determined using modified Bond’s method using ‘reference ore’. Samples of iron ore were sourced using random method, reference minerals; marble and granite of known weight and iron ore of known weight were ground using the laboratory ball mill grinding machine. 80% passing size for the iron ore marble and granite samples were obtained at 100μm sieve size for the feeds and products. The work index of reference minerals; marble and granite were used to calculate the work index of iron ore. The value of 28.66 Kwh/short ton and 24.92 Kwh/short ton were obtained. The value of 20.39 Kwh/short ton was selected as it is within the range indicated by previous research work on iron ore in Nigeria.

Alternative Approaches for Determination of Bond Work Index on Soft and Friable Partially Laterised Khondalite Rocks of Bauxite Mine Waste Materials

PLK (Partially Laterised Khondalite) rock is a general terminology used in this paper for those rocks which are in general associated in bauxite mining such as Partially Altered Khondalite (PAK) rocks, Partially Kaolinised Khondalite (PKK) rocks and Lithomerge. This paper deals with the Bond’s work index, Hardgrove index and Brittleness tests on six typical rock samples and its correlation. As a fast method, the determination of the Bond index from the Hardgrove index (by calculation) is almost matching with measured Bond’s work index. The Bond’s work index of the above rock samples calculated from the Hardgrove index value has shown a variation from 7.7 to 10.3 kWh/sh.t. A correlation is found between the friability value and work index. The correlation coefficient of 0.93 between the friability value (S1) and Bond’s work index, Wi = -18.193 Ln (S1) + 66.747 has been found. The brittleness test results may not be very close to the work index values, as in brittleness tests relatively large grains are ground, whereas the HGI values, grinding of fine –grain samples involved. Thus the grindability of PLK rocks or bauxite can be determined by the simple test performance, HGI.

Effect of process parameters on the grindability and Bond index of bauxites and alumina-bearing ores

A specially designed laboratory model of a universal Hardgrove mill was used to study the grindability and Bond-work index of a wide range of bauxites and other alumina-bearing ores. The method of investigation that was used conforms to the standards ASTM D409, ISO 5074 1980, and BS:1016 Part 20 1980. The resulting values make it possible to rank bauxites based on their grindability. An attempt was made to correlate this characteristic with the mineralogical composition and textural-structural features of bauxite. A single method was used to obtain reference values of the Bond-work index of bauxites from most of the mines in the world. Temperature, grinding conditions, and other factors have a significant effect on the grinding of bauxites. The method developed in this study makes it possible to select operating regimes with allowance for the mechano-chemical reactions that take place. The method can also be used to speed up the grinding operation. The completed study showed that the accessibility of the measurements and the use of a lightweight sample in the method employed to simulate the industrial grinding of bauxites are two features that can be put to good use in the design of new, more powerful grinding equipment and the optimization of existing units. This will yield significant savings in terms of both capital investment and operating costs , i.e., a decrease in the amount of energy needed for grinding. Studies made of the grindability of Guinea bauxites (from the ore regions of Kindiya, Friya, and Dian-Dian) under different conditions (dry grinding, wet grinding in water and a commercial alkali-aluminate solution within a broad range of temperatures) have made it possible to more reliably select grinding equipment in the modernization and design of wet-grinding sections as part of projects that are currently under way.

Procedure for determination of ball Bond work index in the commercial operations

The Bond ball mill grindability test is run in a laboratory until a circulating load of 250% is developed. It provides the Bond Ball Mill Work Index which expresses the resistance of material to ball milling. This happens after 7–10 grinding cycles, which shows that the procedure is a lengthy and complex one and is therefore susceptible to procedural errors. Starting from the first-order grinding kinetics defined by means of the Bond ball mill, this paper discusses a simplified procedure for a rapid determination of the work index by just two grinding tests. The applicability of the simplified procedure has been proved on samples of copper and Iron ores that are located in Iran. The values obtained by this procedure do not differ by more than 7% from those obtained in the standard Bond test.