Comminution of Copper Ores with the Use of a High-Pressure Water Jet

energies

Article Comminution of Copper Ores with the Use of a High-Pressure Water Jet

Przemyslaw J. Borkowski Faculty of Geo Engineering Mining and Geology, Wroclaw University of Technology, 50-370 Wroclaw, Poland; [email protected]

Received: 4 November 2020; Accepted: 27 November 2020; Published: 28 November 2020

Abstract: The article presents research on the comminution of copper ore in a self-constructed mill using high-pressure water jet energy to investigate the usefulness of such a method for comminuting copper ore. As a result, ore particles are obtained that are characterized by appropriate comminution and a significant increase in their specific surface, in turn allowing for potential further processing of the mineral. A comparative analysis of the efficiency of copper ore comminution, primarily taking into account the unit energy consumption and the efficiency of the milling process, clearly indicates that the energy absorption of hydro-jet material comminuting is lower than during mechanical grinding, e.g., in a planetary ball mill. The applicability of the technique depends on the brittle nature of the host rock, e.g., it is especially appropriate for sandstone and shale ores.

Keywords: copper ore comminution; hydro-jet mill; high-pressure water jet

1. Introduction Shredding processes are widely used in various fields of raw material processing. Such procedures are carried out in order to lower the costs of maintaining the cutter discs used in Tunnel Boring Machines (TBM) operating in hard rock formations [1]. They are also used to obtain fine-grained particles, sometimes even nanoparticles [2] or those that have an increased specific surface, which can be especially useful in pharmaceuticals [3]. Much attention is paid to the technical aspects of grinding specific mineral materials such as hard rock ores. For example, low-grade hematite ores generally only undergo crushing and screening, which is not energy intensive. Consequently, fine-grained magnetite ores require fine grinding, often to below 30 µm, to liberate the magnetite from the silica matrix, which usually involves traditional techniques. These processes generate greater costs and require higher energy consumption. The need to lower energy consumption is an issue stressed in the literature [4]. The discussion on the concept of dry and wet copper ore grinding in an electromagnetic mill (EMM) also focuses on the efficiency-related advantages of the former from the perspective of both different process parameters and also the energy costs [5,6]. However, a comparison of the results of EMM dry grinding with the results obtained using other standard solutions presented in the publication points to certain advantages of such a processing method. The authors of the above publications also indicate that the presence of sharp edges and the estimation of the processing time required to obtain a product of specific grain size remain a challenge and need further research. Some other authors observe that reducing the size of minerals is the most critical step preceding their final separation. These authors refer to the fundamentals of the crack development processes and see them as being essential for optimizing both the comminution processes and the design of the comminution machines. They conclude that although many advances have been made in the design of comminution machines, the combined effect of crack development processes and ore properties such as ore texture is neither fully understood nor quantified [7].

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An interesting and detailed comparative investigation of the behavior of ores processed in jaw, cone as well as hammer crushers, and in ball mills, was used to investigate the effects of comminution for different samples of chromite ores. The results served as the basis to analyze particle size distributions (PSD) for the products of grinding in order to evaluate the suitability of the Gates–Gaudin–Schuhmann (GGS) and Rosin–Rammler (RR) models. The results suggest that the particle size distributions depend mostly on the applied method of crushing. On the other hand, it was found that the particle size distributions of all chromites subjected to jaw and cone fragmenting were better characterized by the Gates–Gaudin–Schuhmann model than by the Rosin–Rammler model [8]. Another investigation focuses on determining the selection function parameters which describe the effect of the ball size on the milling rate. The investigation illustrates the issue with experiments conducted on coal. The identified balanced ball mixture was taken in order to analyze the effect of ball size distribution on the selection function, while an adequate mixture recommended by the manufacturer of the original equipment was taken to validate the model. The results show that the estimated parameters can be used with confidence for identification of the optimal distribution of balls for a series of operational restrictions [9]. In yet another study, the matrix model and the probability of breakage of the population balance model, were combined with the use of a MATLAB code. Such procedure let to predict the size distribution of the comminution products for different minerals. The resulting models were good well corelated with the particle size distributions achieved from a ball mill [10]. The literature also mentions research aimed at identifying the ball mill grinding characteristics for hematite products comminuted with the use of a high-pressure grinding roll (HPGR) and a traditional cone crusher (CC), focusing mostly on comminuting kinetics and technical efficiency [11]. Compared with CC products, HPGR products were comminuted faster and with an earlier occurrence of the phenomenon of over-grinding fine particles [11]. Analogical conclusions come from the analysis of high-pressure grinding conducted as part of another research project, in which copper ores were crushed by a jaw crusher and a high-pressure grinder, with the products being exposure by means of X-ray tomography. The analysis pointed out that the products from the high-pressure grinding have more particle damage and higher copper recoveries when compared with the jaw crusher [12]. Yet another research identified the mineralogical characteristics of comminuted Sn-Ta ore. The grinding process, carried out with the use of a HPGR in combination with a ball mill (BM), was confronted with a single ball mill process [13]. The combined method reduces the particle size distribution, and as a result helps to increase the flotation effect. The method of dynamic comminution of brittle materials using a high-pressure water jet (HPWJ) is of particular importance here. Particles of material lifted by the water jet at high speed, during collision with a hard disc, are cracked and the resulting gaps are wedged due to water squeezing into them. The intensive fragmentation of particles, which occurs in such conditions, is caused by the fact that tensile stresses arise inside them, and also that brittle materials are much less resistant to these stresses [14,15]. The purpose of this article is to investigate the usefulness of such a high-pressure hydro-jetting method for comminuting specific brittle materials, e.g., copper ores, in order to analyze their susceptibility to micronization, which precedes the flotation process of copper recovery.

2. Mineralogical Characteristics of Copper Ores The deposit of copper ore taken into consideration in this paper is owned by KGHM Polska Miedz mining company. It is situated in the south-west part of Poland and dips from 700 m up to 1500 m. Sandstone, dolomite as well as shale types of rock are characteristic for this deposit, which includes copper minerals. After extraction, copper ore is enriched during mechanical processing composed of crushing, milling and after classifying, undergo flotation. Final procedure are thickening and drying of a Energies 2020, 13, 6274 3 of 11 concentrate. As a result, a concentrate with a 23% copper content is produced that can be processed further in a smelter. Presently, the concentration of copper in ores ranges from 0.95 to 2.6%, depending on the KGHM miningEnergies 2020 region, 13, x andFOR PEER the REVIEW type of ore. As far as the mineralization of carbonate ores is3 of concerned, 11 sulphides can be found as fine, irregular inclusions occurring in the form of nodules and veinlets. Presently, the concentration of copper in ores ranges from 0.95 to 2.6%, depending on the KGHM Themining average region content and the of thetype Cu of inore. the As carbonate far as th rockse mineralization equals 0.8% of [carbonate16]. ores is concerned, sulphidesThe grade can be of found the sandstone as fine, irregular ore can inclusions range from occurring 0.7% Cu in up the to form 30% of Cu nodules but the and average veinlets. number is 1.8%The ofaverage Cu. Sulphides content of occurthe Cu in in thethe formcarbonate of fine rocks anhedral equals 0.8% and [16]. subhedral grains 20 up to 30 µm in size, and asThe aggregates grade of the coming sandstone as interstitial ore can range pore from fillings 0.7% [16 Cu,17 up]. to 30% Cu but the average number is 1.8%The of last Cu. shale Sulphides ore type occur has in the more form complex of fine anhedral mineral and characteristics. subhedral grains The 20 content up to 30 of μ Cum in minerals usuallysize, and exceeds as aggregates 4% in coming weight. as Theinterstitial chalcocite pore fillings and bornite [16,17]. as well as chalcopyrite associations are dominantThe there.last shale The ore minerals type has of more the chalcocitecomplex mineral group characteristics. predominate atThe the content Lubin of area Cu whileminerals the region ofusually Sieroszowice exceeds mine4% in isweight. characterized The chalcocite mostly and by bo digeniternite as andwell chalcociteas chalcopyrite occurrence, associations and are bornite or dominant there. The minerals of the chalcocite group predominate at the Lubin area while the region chalcopyrite being negligible [18]. of Sieroszowice mine is characterized mostly by digenite and chalcocite occurrence, and bornite or chalcopyrite being negligible [18]. 3. Equipment and Research Methodology 3. EquipmentAn analysis and of Research several appliedMethodology design solutions of hydro-jetting mills [19–21], including vertical and horizontalAn analysis designs, of several as applied well as design different solutions comminution of hydro-jetting mechanisms, mills [19–21], allowed including us tovertical develop and buildand horizontal our own constructionaldesigns, as well solutionas different in commin the formution of amechanisms, vertical hydro-jet allowed mill us to (Figure develop1 ).and It build provides the possibilityour own constructional to comminute solution materials in the in theform pressure of a vertical range hydro-jet of 50–300 mill MPa (Figure with 1). a variableIt provides water the flow in thepossibility range 0.2–0.5 to comminute dm3/s. Thismaterials device in the can pressure be used range to comminute of 50–300 MPa brittle with materials a variable having water flow a grain in size of upthe to range 2 mm, 0.2–0.5 and withdm3/s. a This significantly device can increased be used to micronization comminute brittle effi materialsciency, at having the level a grain of 50 size g/ sof [ 22]. up to 2 mm, and with a significantly increased micronization efficiency, at the level of 50 g/s [22].

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Figure 1. General view of experimental setup (a), and a diagram of a hydro-jet mill (b): 1—high-pressure Figure 1. General view of experimental setup (a), and a diagram of a hydro-jet mill (b): 1—high- pump, 2—manometer, 3—water nozzle, 4—comminuting nozzle, 5—comminuting disk, 6—shredding pressure pump, 2—manometer, 3—water nozzle, 4—comminuting nozzle, 5—comminuting disk, 6— chamber, 7—feed tank, 8—product tank, 9—water tank. shredding chamber, 7—feed tank, 8—product tank, 9—water tank.

TheThe tests covered covered three three types typesof copper of ores copper found ores in the found KGHM in (Poland) the KGHM mines (carbonate, (Poland) mines (carbonate,sandstone and sandstone shale). These and shale). three types These of threeore were types first of mechanically ore were first ground mechanically in a jaw crusher ground to in a jaw crusherobtain togranules obtain granulesof the required of the particle required size particle # 0.5–2 size mm, # 0.5–2 which mm, were which subsequently were subsequently subjected to subjected tocomminution comminution with with a high-pressure a high-pressure water water jet, i.e., jet, to i.e., the to process the process being the being focus the of focus this article. of this article. AA FEI FEI Quanta Quanta 200200 Mark II II scanning scanning microscope microscope was was used used to assess to assess the shape the shape and morphology and morphology of theof copperthe copper ore ore particles. particles.

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MeasurementsEnergies 2020, 13 of, x the FOR fragmentation PEER REVIEW effects of the studied ores were carried out using the Analysette4 of 11 22 MicroTec Plus particle size laser meter, which allows the analysis and preparation of particle size distributionsMeasurements of 0.08–2000 µ ofm. the fragmentation effects of the studied ores were carried out using the TestsAnalysette of the effi 22ciency MicroTec of hydro-jetting Plus particle comminutionsize laser meter, of which copper allows ore werethe analysis carried and out: preparation of particle size distributions of 0.08–2000 μm. at a nominalTests waterof the efficiency pressure of hydro-jetting 100, 150, 200 co andmminution 250 MPa, of copper ore were carried out: • with• a diameter of the water nozzle dw = 0.7 mm, • at a nominal water pressure of 100, 150, 200 and 250 MPa, using• a comminuting nozzle diameter d =w 2.4 mm, • with a diameter of the water nozzleh d = 0.7 mm, with• a distanceusing a between comminuting the outlet nozzle of thediameter homogenizing dh = 2.4 mm, nozzle and the comminuting disc: s = 10 mm. • • with a distance between the outlet of the homogenizing nozzle and the comminuting disc: s = 10 mm. Depending on the needs, the number of parallel measurements ranged from 5 to a dozen or so Depending on the needs, the number of parallel measurements ranged from 5 to a dozen or so trials, and their averaged results formed the basis for assessing the analyzed quantities. trials, and their averaged results formed the basis for assessing the analyzed quantities. 4. Hydro-Jet Milling of Copper Ores 4. Hydro-Jet Milling of Copper Ores Tests of hydro-jetting comminution of three different types of copper ore yielded results in the Tests of hydro-jetting comminution of three different types of copper ore yielded results in the form of particleform of particle distributions, distributions, an example an example of which of which is shown is shown in Figure in Figure2. 2. The testsThe were tests carried were carried out at out the at nominal the nominal pressure pressure of theof the water water jet, jet, and and appliedapplied in in the the range range of ofp 3 p = 100–250= 100–250 MPa with MPa anwith output an output of Qw of= Q0.2–0.5w = 0.2–0.5 dm dm/s.3/s. The The samples samples consisted consisted of of individual individual batchesbatches of of m = 1 kgm of = copper 1 kg of ore, copper and theore, comminutingand the comminuting time (t) wastime also (t) was measured. also measured. For such For conditions, such conditions, the copper the ores werecopper found ores to show were afound relatively to show high a resistancerelatively high to comminution. resistance to comminution. However, different However, results different were obtainedresults for different were obtained ore types. for The different efficiency ore types. of the The process, efficiency assessed of the on process, the basis assessed of the reduction on the basis ofthe of dimensionsthe ofreduction particles of obtained the dimensions in the processof particles of hydro-jet obtained milling,in the process is illustrated of hydro-jet by the milling, graphs is illustrated presented by the graphs presented in Figure 3. The influence of water jet pressure on the change in the passing in Figure3. The influence of water jet pressure on the change in the passing size of the ore particles (a 90) size of the ore particles (a90) is marked by the solid line, and the dotted line presents the efficiency is marked by the solid line, and the dotted line presents the efficiency (Qc) of the milling process. (Qc) of the milling process. The research conducted on copper ores generally shows that as the nominal water pressure The research conducted on copper ores generally shows that as the nominal water pressure increases,increases, the efficiency the efficiency of micronization of micronization also increases,also increases, the the phenomenon phenomenon of of which which is is assessed assessed on the basis of thebasis increasingly of the increasingly smaller particle smaller sizes particle obtained sizes fromobtained hydro-jet from milling.hydro-jet Moreover, milling. Moreover, the efficiency the of such millingefficiency also of increases.such milling also increases. A detailedA detailed analysis analysis of these of charts these shows charts thatshows the that courses the courses for individual for individual types oftypes copper of copper ore differ. ore In the casediffer. of the In carbonatethe case of ore,the carbonate for a water ore, jet for pressure a water of jet 100 pressure MPa, of the 100 maximum MPa, the characteristicmaximum characteristic grain size for 90% ofgrain the size fragmented for 90% of ore the particles fragmented is a 90ore= particles130.7 µ m,is a for90 = a130.7 pressure μm, for of a 150 pressure MPa itof is 150a90 MPa= 75.2 it isµ am90 , = 75.2 μm, and for a pressure of 200 MPa it is equal to a90 = 63.8 μm. For the highest applied jet pressure and for a pressure of 200 MPa it is equal to a90 = 63.8 µm. For the highest applied jet pressure (250 MPa), (250 MPa), the maximum particle size would be a90 = 49.4 μm. The efficiency of the hydro-jet the maximum particle size would be a90 = 49.4 µm. The efficiency of the hydro-jet comminuting process, comminuting process, however, is respectively: 15.1 g/s for the pressure of 100 MPa, 16.9 g/s for the however, is respectively: 15.1 g/s for the pressure of 100 MPa, 16.9 g/s for the pressure of 150 MPa, pressure of 150 MPa, 18.4 g/s for 200 MPa, and 22.4 g/s for the maximum pressure of the water jet 18.4 g/s for 200 MPa, and 22.4 g/s for the maximum pressure of the water jet (250 MPa). (250 MPa).

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(b)

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FigureFigure 2. Example2. Example of of the the distribution distribution of of three three types types of of copper copper oreore comminutedcomminuted in a hydro-jet hydro-jet mill mill at a Figure 2. Example of the distribution of three types of copper ore comminuted in a hydro-jet mill at a at awater water pressure pressure of 150150 MPa:MPa: (a()—carbonate,a)—carbonate, ( b()—sandstone,b)—sandstone, (c )—shale(c)—shale ore, ore, performed performed using using the the water pressure of 150 MPa: (a)—carbonate, (b)—sandstone, (c)—shale ore, performed using the Analysette 22 MicroTec Plus particle laser meter. AnalysetteAnalysette 22 MicroTec 22 MicroTec Plus particle Plus particle laser meter. laser meter.

(a) (a)

Figure 3. Cont.

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(b)

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Figure 3. Influence of water jet pressure on the efficiency of the comminution (of characteristic Figure 3. Influence of water jet pressure on the efficiency of the comminution (of characteristic dimensions) for 90% of ground copper ore particles (a90), and the efficiency (Qc) of its milling process dimensions) for 90% of ground copper ore particles (a90), and the efficiency (Qc) of its milling process for: (a)—carbonate, (b)—sandstone, (c)—shale ore. for: (a)—carbonate, (b)—sandstone, (c)—shale ore.

The second type of sandstone copper ore has the following maximum grain sizes: a90 = 121.8 µm The second type of sandstone copper ore has the following maximum grain sizes: a90 = 121.8 μm for a water jet pressure of 100 MPa, a90 = 102.5 µm for 150 MPa, a90 = 91.9 µm for 200 MPa, for a water jet pressure of 100 MPa, a90 = 102.5 μm for 150 MPa, a90 = 91.9 μm for 200 MPa, and a90 = and a = 83.7 µm (the minimum size) for the highest jet pressure (250 MPa). The efficiency of the 83.790 μm (the minimum size) for the highest jet pressure (250 MPa). The efficiency of the sandstone sandstone copper ore hydro-jet comminuting process can be described with the following values: copper ore hydro-jet comminuting process can be described with the following values: 20.1 g/s for a 20.1 g/s for a pressure of 100 MPa, 29.7 g/s for a pressure of 150 MPa; 34.6 g/s for 200 MPa, and 35.6 g/s pressure of 100 MPa, 29.7 g/s for a pressure of 150 MPa; 34.6 g/s for 200 MPa, and 35.6 g/s for the for the maximum pressure of the water jet (250 MPa). maximum pressure of the water jet (250 MPa). The last studied type was shale copper ore. The experiments allowed the degree of its fragmentation The last studied type was shale copper ore. The experiments allowed the degree of its to be estimated at a90 = 49.1 µm for 100 MPa. Higher values of water jet pressure, such as 150 MPa, fragmentation to be estimated at a90 = 49.1 μm for 100 MPa. Higher values of water jet pressure, such as cause the maximum particle size to decrease to a90 = 44.7 µm, and for the level of 200 MPa, it is 150 MPa, cause the maximum particle size to decrease to a90 = 44.7 μm, and for the level of 200 MPa, it even slightly lower, reaching a90 = 43.8 µm. The use of the highest water jet pressure of 250 MPa is is even slightly lower, reaching a90 = 43.8 μm. The use of the highest water jet pressure of 250 MPa is uneconomical as it causes relatively insignificant changes in the maximum dimension a90 = 42.6 µm, uneconomical as it causes relatively insignificant changes in the maximum dimension a90 = 42.6 μm, which is characteristic for 90% of the fragmented ore particles. Considering the efficiency of the which is characteristic for 90% of the fragmented ore particles. Considering the efficiency of the hydro- hydro-jet comminuting of copper shale ore, it should be noted that it increases with the increase of the jet comminuting of copper shale ore, it should be noted that it increases with the increase of the nominal nominal water pressure, reaching the efficiency of 32.0 g/s for a pressure of 100 MPa. In turn, for a water pressure, reaching the efficiency of 32.0 g/s for a pressure of 100 MPa. In turn, for a pressure of pressure of 150 MPa it is 32.7 g/s, for 200 MPa it is 35.2 g/s, and for the maximum water jet pressure of 150 MPa it is 32.7 g/s, for 200 MPa it is 35.2 g/s, and for the maximum water jet pressure of (250 MPa) (250 MPa) considered in the tests, the efficiency of this process reaches the value of 36.8 g/s. considered in the tests, the efficiency of this process reaches the value of 36.8 g/s. Copper ore particles formed during hydro-jet comminution are usually characterized by an Copper ore particles formed during hydro-jet comminution are usually characterized by an isometric shape with fairly expressive edges, while their rough surface usually takes the form of highly isometric shape with fairly expressive edges, while their rough surface usually takes the form of developed spatial micro-openings for a carbonate ore (a), a multiple trimming effect for sandstone (b), highly developed spatial micro-openings for a carbonate ore (a), a multiple trimming effect for or a relatively smooth surface for shale ore. This is best characterized by the SEM images shown in sandstone (b), or a relatively smooth surface for shale ore. This is best characterized by the SEM Figure4, which illustrate typical examples of their shape and morphology. images shown in Figure 4, which illustrate typical examples of their shape and morphology.

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((aa)) ((bb)) ((cc))

Figure 4. Examples of SEM images of copper ore particles comminuted in a hydro-jet mill at a water jet pressureFigureFigure 4.4. of ExamplesExamples 150 MPa: ofof (a SEM)—carbonate,SEM imagesimages ofof (b coppercopper)—sandstone, oreore particlesparticles (c)—shale comminutedcomminuted ore. inin aa hydro-jethydro-jet millmill atat aa waterwater jetjet pressurepressure ofof 150150 MPa:MPa: ((aa)—carbonate,)—carbonate, ((bb)—sandstone,)—sandstone, ((cc)—shale)—shale ore.ore. The comparison of the above photos with analogous scan pictures of the same three types of copperTheThe ore comparisoncomparison comminuted ofof thethe in a aboveabove PM 100 photosphotos type withwith laboratory analoganalogous planetaryous scanscan picturespictures ball mill ofof (Figure thethe samesame5) is threethree interesting. typestypes ofof Thecoppercopper surface oreore comminutedcomminuted quality of the inin aa copper PMPM 100100 ore tytypepe particles laboratorylaboratory obtained planetaryplanetary as a ballball result mimillll of (Figure(Figure the mechanical 5)5) isis interesting.interesting. grinding TheThe operationssurfacesurface qualityquality is significantly ofof thethe coppercopper diff oreoreerent. particlesparticles The surface obtainedobtained of such asas aa resultresult particles ofof thethe is generally mechanicalmechanical devoid grindinggrinding of any operationsoperations cavities andisis significantlysignificantly is characterized different.different. by a relatively TheThe surfacesurface high ofof smoothness, suchsuch particlesparticles which isis probablygenerallygenerally causes devoiddevoid certain ofof anyany problems cavitiescavities in andand their isis echaracterizedcharacterizedffective enrichment byby aa relatively inrelatively the flotation highhigh process.smoothness,smoothness, If other whwh methodsichich probablyprobably of mechanical causescauses certaincertain grinding problemsproblems of copper inin ores,theirtheir especiallyeffectiveeffective enrichmentenrichment those used ininin actual thethe flotationflotation production process.process. processes, IfIf otherother provide methodsmethods powders ofof mechanicalmechanical of similar grindinggrinding quality, ofof the coppercopper suitability ores,ores, ofespeciallyespecially the industrial thosethose technologies usedused inin actualactual used productionproduction so far should procproc beesses, carefullyesses, provideprovide analyzed. powderspowders ofof similarsimilar quality,quality, thethe suitabilitysuitability ofof thethe industrialindustrial technologiestechnologies usedused soso farfar shouldshould bebe carefullycarefully analyzed.analyzed.

((aa)) ((bb)) ((cc))

Figure 5. Examples of SEM images of copper ore particles comminuted in a planetary ball mill type PMFigureFigure 100: 5.5. (a ExamplesExamples)—carbonate, ofof SEMSEM (b)—sandstone, imagesimages ofof coppercopper (c)—shale oreore particlesparticles ore. comminutedcomminuted inin aa planetaryplanetary ballball millmill typetype PMPM 100:100: ((aa)—carbonate,)—carbonate, ((bb)—sandstone,)—sandstone, ((cc)—shale)—shale ore.ore. 5. Results Discussion 5.5. ResultsResultsAn essential DiscussionDiscussion feature of each production process is the energy expenditure necessary for its implementation.AnAn essentialessential In featurefeature order to ofof determine eacheach productionproduction the energy procesproces consumptionss isis thethe energy ofenergy the process expenditureexpenditure of comminuting necessarynecessary copper forfor itsits ore,implementation.implementation. relevant tests In wereIn orderorder carried toto determinedetermine out in ahydro-jet thethe energyenergy mill coco and,nsumptionnsumption for comparison ofof thethe processprocess purposes, ofof comminutingcomminuting also in a planetary coppercopper ballore,ore, mill relevantrelevant type teststests PM 100. werewere The carriedcarried unit out energyout inin aa consumption hydro-jethydro-jet mmillillof and,and, hydro-jet forfor comparisoncomparison comminution purposes,purposes, is calculated alsoalso inin aa according planetaryplanetary toballball formula millmill typetype (1), PMPM while 100.100. the TheThe adequate unitunit energyenergy consumption consumptionconsumption for a ofof planetary hydro-jethydro-jet ball comminutioncomminution mill is described isis calculatedcalculated by (2). accordingaccording toto FormulaFormula (1),(1), whilewhile thethe adequateadequate consumptionconsumption forfor aa planetaryplanetary ballball millmill isis describeddescribed byby (2).(2). p Qw t E = (1) 𝑝𝑝m 𝑄𝑄 𝑡𝑡 𝐸=𝐸= (1)(1) 𝑚𝑚 where: p—water pressure, Qw—water output, t—time of comminuting the batch of copper ore, mwhere:where:—weight p—p—water ofwater copper pressure,pressure, ore batch; QQww—water—water output,output, tt—time—time ofof comminutingcomminuting thethe batchbatch ofof coppercopper ore,ore, mm—— weightweight ofof coppercopper oreore batch;batch;

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𝑃 𝑡 P t E =𝐸= (2) m 𝑚 where:where:P—power p- power of of the the planetary planetary ball ball mill. mill. InterestingInteresting eff ectseffects resulting resulting from from the the conducted conducted tests test ares presented are presented in Figure in Figure6. In general, 6. In general, using theusing sizethe of size the carbonateof the carbonate copper orecopper particles ore particles obtained obta in theined process in the of process their comminution of their comminution as a common as a criterioncommon for criterion the different for the methods different of comminutionmethods of comminution analyzed in this analyzed article in made this itarticle possible made to compareit possible theto unit compare energy the consumption unit energy ofconsumption these processes. of these processes. TheThe charts charts indicate indicate the the points points for for which which joint joint tests te withsts with the the use use of both of both methods methods of comminution of comminution of suchof oresuch were ore carried were out.carried As aout. result, As it a was result, possible it was to make possible unit comparisonsto make unit of energycomparisons consumption of energy in theconsumption two tested methods. in the two In thetested case methods. of carbonate In the copper case oreof carbonate (Figure6a), copper the specific ore (Figure energy 6a), consumption the specific ofenergy hydro-jet consumption comminuting of ishydro-jet two to five comminuting times more is favorable two to five than times when more using favorable a mechanical than when planetary using balla mechanical mill. The same planetary characteristics ball mill. are The presented same characteristics for the sandstone are presented ore (Figure for6b) the and sandstone show the ore highest (Figure advantage6b) and ofshow hydro-jetting the highest at aadvantage level approximately of hydro-jetting 40 times at higher. a level Consequently, approximately the 40 comparison times higher. of theConsequently, energy consumption the comparison of the two of appliedthe energy shale cons oreumption comminuting of the two methods applied (Figure shale6 c)ore again comminuting points tomethods the more (Figure favorable 6c) resultsagain ofpoints the hydro-jetto the more method. favorable This confrontationresults of the proveshydro-jet that method. the energy This consumptionconfrontation of proves the proposed that the method energy consumption of hydro-jet comminuting of the proposed is generallymethod of three hydro-jet and acomminuting half times loweris generally than in thethree case and of thea half mechanical times lower grinding than methodin the case in a of planetary the mechanical ball mill. grinding method in a planetaryThe use ball of anothermill. criterion for comparing the energy consumption of material comminuting processesThe is use not of possible another duecriterion to the for use comparing of completely the energy different consumption milling methods. of material When comminuting using a mechanicalprocesses planetaryis not possible ball mill, due the to grindingthe use of thecomp feedletely occurs different as a result milling of the methods. dynamic When interaction using a ofmechanical the ball grinding planetary elements. ball mill, Therefore, the grinding extending of the feed the operationoccurs as a time result of of such the adynamic mill contributes interaction toof an the increased ball grinding efficiency elements. of the Therefore, milling process extending by the causing operation greater time fragmentation of such a mill of contributes the particles to an (i.e.,increased reducing efficiency their dimensions). of the milling In such process circumstances, by causing forgreater the given fragmentation conditions of and the for particles the given (i.e., equipmentreducing oftheir the mill,dimensions). the impact In of such the e ffcircumstanectiveness ofces, the for milling the given process conditions on the energy and consumptionfor the given ofequipment the material of grinding the mill, mainly the dependsimpact of on the the durationeffectiveness of this of process. the milling process on the energy consumptionCompletely of di thefferent material relations grinding occur mainly in the depends conditions on the of duration comminuting of this materialsprocess. (including copperCompletely ore) using adifferent high-pressure relations water occur jet. in In the a hydro-jetconditions mill, of comminuting materials of the feed (including occurs ascopper a result ore) of theusing synergistic a high-pressure interaction water of jet. a high-pressure In a hydro-jet water mill, jetcomminuting and the dynamic of the feed impact occurs of the as a particlesresult of undergoing the synergistic comminution. interaction Therefore, of a high-pressure in such circumstances, water jet and for the the dynamic given conditions impact of and the millparticles equipment, undergoing the effi ciencycomminution. of the comminution Therefore, in process such circumstances, of the batch, assessedfor the given on the conditions basis of the and reductionmill equipment, of the dimensions the efficiency of theof the obtained comminution particles, process is primarily of the batch, determined assessed by on the the level basis of of the the nominalreduction water of pressure.the dimensions of the obtained particles, is primarily determined by the level of the nominal water pressure.

(a)

Figure 6. Cont.

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(b)

(c)

Figure 6. Dependence of the unit energy consumption of copper ore comminution on the efficiency of itsFigure milling 6. processDependence in a high-pressure of the unit energy hydro-jet consumption mill (1) and of copper in a planetary ore comminution ball mill type on the (2) PMefficiency 100 1 (nof= 5its s −milling) for carbonate process in copper a high-pre ore (ssurea), sandstone hydro-jet (b mill) and (1) shale and orein a (planetaryc). ball mill type (2) PM 100 (n = 5 s−1) for carbonate copper ore (a), sandstone (b) and shale ore (c). By properly confronting the energy consumption results of comminuting with both methods, presentedBy properly in the form confronting of the two the curves energy in consumption Figure6, it was results found of thatcomminuting the energy with consumption both methods, of hydro-jetpresented comminuting in the form of the copper two orecurves is distinctly in Figure smaller 6, it was than found during that mechanicalthe energy consumption grinding in a of planetaryhydro-jet ball comminuting mill. The resulting of copper benefits ore is are distinctly determined smaller by the than following during indicator: mechanical grinding in a planetary ball mill. The resulting benefits are determined by the following indicator: EM Wk = 𝐸 (3) E 𝑊 =H (3) 𝐸 where: EM—energy consumption when crushing copper ore in a planetary ball mill, EH—energy where: EM—energy consumption when crushing copper ore in a planetary ball mill, EH—energy consumption when comminuting copper ore in a hydro-jet mill. consumption when comminuting copper ore in a hydro-jet mill. On the basis of the above dependence, an indicator of benefits occurring in relation to the tested On the basis of the above dependence, an indicator of benefits occurring in relation to the tested conditions of the two compared methods was determined, ensuring in each case equal values of the conditions of the two compared methods was determined, ensuring in each case equal values of the maximum characteristic dimension for 90% of ground ore particles (a90). The determined relationships maximum characteristic dimension for 90% of ground ore particles (a90). The determined allow finding the real values of the indicator of energy-consumption benefits, resulting from the relationships allow finding the real values of the indicator of energy-consumption benefits, resulting comminuting of ore in a hydro-jet mill, as shown in Figure7. With regard to milling in a PM 100 from the comminuting of ore in a hydro-jet mill, as shown in Figure 7. With regard to milling in a PM planetary ball mill, this comminution index in a high-pressure hydro-jet mill is usually very favorable. 100 planetary ball mill, this comminution index in a high-pressure hydro-jet mill is usually very The analysis of the data in this graph indicates that the energy consumption benefit equals an average favorable. The analysis of the data in this graph indicates that the energy consumption benefit equals of 4 for carbonate copper ore (Figure7a), 40 for sandstone copper ore (Figure7b), and 3.5 for shale an average of 4 for carbonate copper ore (Figure 7a), 40 for sandstone copper ore (Figure 7b), and 3.5 copper ore (Figure7c). for shale copper ore (Figure 7c).

Energies 2020, 13, 6274 10 of 11 Energies 2020, 13, x FOR PEER REVIEW 10 of 11

(a) (b) (c)

Figure 7. Values of the indicator of energy consumption benefits that result from the comminution of: Figure(a)—carbonate, 7. Values of (b the)—sandstone, indicator of (c energy)—shale consumption copper ore in be anefits hydro-jet that result mill. from the comminution of: (a)—carbonate, (b)—sandstone, (c)—shale copper ore in a hydro-jet mill. 6. Conclusions 6. ConclusionsConducting detailed analyses of the research results made it possible to draw conclusions that are importantConducting for better detailed understanding analyses of thethe processresearch of results the hydro-jet made it comminution.possible to draw Increasing conclusions the waterthat arejet important pressure has for a better beneficial understanding effect on the the hydro-jetting process of processthe hydro-jet of comminuting comminution. the discussedIncreasing typesthe waterof copper jet pressure ore, as wellhas a as beneficial on the milling effect eonffi ciency.the hydro-jetting A comparative process analysis of comminuting of the efficiency the discussed of copper typesore comminution, of copper ore, primarilyas well as taking on theinto milling account efficiency. the unit A energycomparative consumption analysis andof the the efficiency efficiency of of copperthe milling ore comminution, process, clearly primarily indicates thattaking the into energy account absorption the unit of hydro-jet energy materialconsumption comminuting and the is efficiencynormally of in the the milling range of process, 4~40 times clearly lower indicates than during that the mechanical energy absorption grinding, e.g.,of hydro-jet in a planetary material ball comminutingmill. However, is normally in terms ofin the energyrange of consumption 4~40 times lower of the than process, during the mechanical increase in grinding, water pressure e.g., in is a unfavorable.planetary ball During mill. However, comminution in terms of copper of the oreenergy in a consumption hydro-jet mill, of particles the process, with the a fairly increase regular in waterisometric pressure shape is areunfavorable. usually formed. During Theircomminution most favorable of copper morphology ore in a hydro-jet arises at mill, a water particles pressure with of a 150fairly MPa regular for a carbonateisometric ore,shape while are ausually multiple form trimminged. Their eff mostect can favorable be seen formorphology sandstone arises ore or at for a a waterrelatively pressure smooth of 150 surface—the MPa for a shale carbonate copper ore, ore. wh Furtherile a multiple increasing trimming of the water effect pressure can be seen up to for the sandstonemaximum ore analyzed or for a relatively level of 250 smooth MPa improvessurface—the the shale micro-openings copper ore. Further effect for increasing sandstone of copper the water and pressureshale ore. up This to the knowledge maximum should analyzed be useful level in of the 250 operations MPa improves of the further the micro-openings processing of such effect copper for sandstoneore. For the copper above and reasons, shale theore. hydro-jet This knowledge method, shou whichld usesbe useful a high-pressure in the operations water jet of to the comminute further processingcopper ore of and such other copper brittle ore. materials, For the is above very promising.reasons, the hydro-jet method, which uses a high- pressureAs water the process jet to incomminute the current copper solution ore of and the other high-pressure brittle materials, hydro-jet is millvery (designed promising. by the author) offersAs athe significantly process in lower the current energy consumption,solution of the as high-pressure well as other advantages,hydro-jet mill this (designed prototype by can the be author)seen as offers a competition a significantly for standard lower energy milling consumption, devices that as usewell conventional as other advantages, methods this of mechanicalprototype candisintegration be seen as of a brittle competition materials. for The standard current designmilling solution devices of suchthat ause hydro-jet conventional mill is the methods development of mechanicalbase for the disintegration construction ofof derivative brittle materials. devices The for comminutingcurrent design various solution minerals of such in a a hydro-jet wet environment. mill is the development base for the construction of derivative devices for comminuting various minerals in Funding: This research received no external funding. a wet environment. Conflicts of Interest: The authors declare no conflict of interest. Funding: This research received no external funding.

ConflictsReferences of Interest: The authors declare no conflicts of interest.

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