About Addis Ababa University Institutional Repository (AAU-ETD)
AAU-ETD is an electronic open access institutional repository of Addis Ababa University that makes available and digitally preserves the scholarly outputs produced at AAU. The repository contains both published and unpublished work including: theses and dissertations,preprint,staff and student publications.
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Recent Submissions
Grindability and Comminution Energy Consumption in Case of Midroc (Lega Dembi and Sakaro) Gold Ore
(Addis Ababa University, 2023-09) Yonas Hordofa; Bogale Tadasse (PhD)
The purpose of this study was to investigate the impact of mill speed and grinding time on the grindability and comminution of gold ores from the Lega Dembi and Sakaro deposits. A batch mill internal diameter of 200 mm and volume (5 dm3) was used for the experiment. The study employed a two-factor approach, considering different grinding times (10 and 15 minutes) and three fractions of mill critical speed (40%, 50%, and 60%).The experiment involved dividing the feed into five equal portions across eleven size class fractions ranging from 4mm to -75μm, with a √2-series interval. A total of ten kilograms of material, divided into one-kilogram portions, were used for the experiment. The objective of maintaining a critical speed below or equal to 50% was to minimize energy consumption during the milling process. The study aimed to assess both the grindability and energy consumption of the two deposits. The results of the study indicated that the rate of breakage increased with grinding time rather than mill speed. For the Lega Dembi deposit, at 40%, 50%, 60% speed and 15 minutes grinding time, the amounts of desired particle size classes produced were 251.7 grams, 264 grams, and 263 grams for the different mill speeds. Similarly, for the Sakaro deposit, the amounts produced were 251.7 grams, 232.6 grams, and 256 grams for the respective mill speeds. Based on the obtained results, the study concluded that mill speed had no significant effect on the grindability of the gold ores from both mining sites, as grinding times.
Grindibility and breakage characteristics of Sekota iron ore deposit in Wag-Himra Zone, Northern Ethiopia
(Addis Ababa University, 2023-06) Yohanes Belachew; Bogale Tadesse (PhD); Birtukan Yenealem (Co-Advisor)
In this study, the influence of mill rotation speed and grinding time were investigated on Sekota
iron ore grinding process in a batch mill with length 150 mm and inner diameter 150 mm. The
particle size distribution of the feed was carried out by an electric sieve and the bulk feed was
classified into three samples to perform the grinding test. Three distinct iron ore feed size
fractions between -335mm to +0.71mm, -0.71mm to +0.15mm and -3.35 to -0.075mm separated
by a series of √2 gaps were prepared. The fractions were milled at different grinding times (5,
15, 25, 35, 45 and 60 min) at 450 rpm and at different mill rotational speeds (250, 300, 350, 450
and 550 rpm) at 25 min. The mill rotation speed and grinding time affect the energy
consumption, the desired grind size and the P80 of the feed size fraction. When grinding time
increased from 5 to 60 min, the percentage of cumulative mass of target size increased from 8.5
to 31.1%, from 7.1 to 22.8% and from 10.6 to 26% for coarse, fine and mixed iron ore size
fractions, respectively. Likewise, a significant amount of the desired grind size is produced as the
grinding speed increases until the maximum critical speed is reached. For all feed size fractions,
the required grind size amount (-0.075 mm) is not achieved at grinding times from 5 min to
60 min and at maximum mill rotation speed (450 rpm). The product size distribution of the three
iron ore feed size fractions were also affected as the grinding time and the mill rotation speed
increased from 5 to 60 min and 250 rpm to the maximum speed (450 rpm). The P80 values of all
feed size fraction generally decreased both milling time and mill speed are increased from 5 to
60min and 250 to 450 rpm respectively. Unlike the P80, the energy consumption of the ball mill
increases significantly as the mill speed and grinding time increase from 250 to 450 rpm and
from 5 to 60 minutes respectively.
Evaluation of the Nature of Porosity in Carbonate Rock Of Hamanlei Formation, Ogaden Basin, Ethiopia: Implications For Prediction of Reservoir Quality
(Addis Ababa University, 2023-06) Yimam Ali; Solomon Kassa (PhD)
The Ogaden basin is the largest sedimentary basin in Ethiopia having 350,000 km2 areal
coverage. It is also the most studied sedimentary basin in Ethiopia. Nonetheless, the amount of
data gathered from this baisn is not enough to better comprehend the petroleum system of the
basin. The Hamanlei carbonate rock in the basin makes good reservoir rock. The nature of this
reservoir rock is complex owing to various factors. Despite detail studies were conducted to
understand the reservoir property, particularly core and wireline log study, further studies are
needed for better characterization of this reservoir rock. To further characterize the reservoir
property, i.e. porosity, of this rock and prediction for reservoir quality, petrographic and image
analysis were performed. The outcome of this study provides valuable insights into the
mineralogy and texture of the studied rocks. Furthermore, it highlights the importance of
understanding the different pore types that enables to better interpret the reservoir quality and
potential flow characteristics of the studied rocks. Generally, the porosity value of the reservoir
rock is too small which is caused by the dominant proportion of matrix and cement
Process Mineralogy of Laga Dambi Gold Ore, Oromiya, Southern Ethiopia
(2023-09) Walkite Alemayehu; Bogale Tadesse (PhD)
To understand gold ore processing, the important mineralogical properties of Laga Dambi gold ore was described qualitatively and quantitatively. This is required to determine the parameters of gold ore grade, ore composition (elemental and mineralogical), and concentration of any valuable minerals, nature and concentration of minerals detrimental to the processing. One 75mm x50mm size polished thin section was supplied from each sample and was examined by conventional transmitted and reflected light polarizing microscope to determine the distribution of gold in the samples. Sub samples (500g) of each ore type were ground to 1mm and the heavy minerals concentrated using gold pan. The concentrates were submitted for mineralogical analysis to determine the distribution and particle size of gold in the samples. XRD, XRF and Geochemical analysis was carried out for gold mineralogical characterization and its concentration determination. From the data obtained it can be concluded that, gold is the most valuable element in the ore. The samples are all well graded and show excellent liberation. Sulphide mineralization is coarse within all the samples The pyrrhotite is the most abundant sulphide in all the samples, with the exception of Mse T5 where it is second in abundance to pyrite.Samples OP T1 and MSe T5 containing the highest concentrations of sulphide minerals. The gangue in the samples is dominated by crystalline quartz and mica (muscovite, biotite and phlogopite). Gold was identified in all but the Op T1 head sample. Pyrroyite, pyrite, and chalcopyrite are the most frequent interfering minerals that either consume cyanide or oxygen, or both, and adversely affect the rate or extent of gold leaching. From mineralogical point of view liberation size of gold can be determined to be120μm. from XRD and XRF techniques quartz was predominant gangue minerals in all types. Ankerite, dolomite and plagioclase feldspar were also present in minor constituent. All samples contained low levels of base metals, with the possible exception of OP T3, which are not likely to hinder processing mechanism.
Application of Lapidary Technology for Sustainable Gemstone Resource Development In Ethiopia
(2023-09) Tsion Shumalem; Abubeker Yimam (PhD); Aselefech Mitiku (Ms.)(Co-Advisor)
Ethiopia is renowned for its mineral abundance and more than 40 varieties of gemstone resources. With the artisanal and small scale miners controlling the production, the phase of the gemstone path abruptly came to a halt, with just a few rough dealers and a few gem cutters remaining, resulting in a very low economic benefit from the sector. The purpose of this study is to look into the function of lapidary technology for sustainable gemstone resource development in Ethiopia. The paper focuses on identifying the country‘s gemstone resource development challenges, the stages of the lapidary process and colored gemstone value chains, lapidary technology and the economic and social importance of lapidary technology in creating various jewelry and decorations using the new technology. In this study, interviews, literature reviews, lapidary work on a selected sample (gemstone from Wegel Tena, Amhara Regional State, Ethiopia), and an economic analysis of rough and value-added gems are conducted to analyze the role of lapidary technology on the industry. Furthermore, it is designed to comprehend the stages of the supply process and gem value chain, as well as to investigate the economic and social ramifications of modern lapidary technology on the development of sustainable gemstone resources. The impact of lapidary on increasing the value of rough gemstones is enormous. An economic analysis made of agate, crystal quartz, obsidian, jasper, and opal found that there is an increase between 400 and 70,000 folds due to the effect of lapidary technology and value added on the rough gemstone. The study’s findings revealed that the fragmented character of the gemstone business attributed to its lag behind other mining industries. Moreover, the study indicated that the gemstone industry in Ethiopia lacks technology, finance, lapidary expertise and a controlled market system. Enabling legislation should be put in place to ensure that the necessary economic return from gemstone resources is attained in order to protect the business and support a successful gemstone cutting and polishing industry.