high quality gold processing ball mill from xinhai

mineral processing, equipment manufacturers, ball mills, flotation, thickener - xinhai

mineral processing, equipment manufacturers, ball mills, flotation, thickener - xinhai

The new grooved annular liner increases the ball ore contact surface, strengthens the grinding effect, and has the ability to lift the ore, reducing energy consumption; the large double-row spherical roller bearing design can reduce the friction.

An air inflation mechanical agitation floatation cell with slurry suction, which is featured with strong agitation force, good air spreading effect, uniform mixing of slurry and air, less sedimentary of tailings, low turnaround speed and low power consumption.

This thickener is a new type thickening equipment independently developed by Xinhai. The thickener is equipped with additional deaerating tank, which can eliminate the solid particles attaching to the bubbles.

A double stages slurry pump with head of 70m. It is lined with high wear-resisting rubber, whose abrasion resistance index is up to 128%. Double Stages Slurry Pump is a rare rubber slurry pump with integrated effects of wear-resisting, anticorrosion and high head.

The Mongolia 1,000t/d gold mineral processing plant was an EPC+M+O project. Xinhai worked to achieve high recovery of gold and other valuable minerals by cutting costs and maximizing benefits and attach great importance to workers safety, environmental protection and energy conservation.

Mexico 1500t/d copper lead zinc gold and silver polymetallic ore dressing project is a mining industry chain service (EPC + M + O) project undertaken by xinhai, which is solely undertaken by xinhai from design and research, manufacturing and procurement of complete sets of equipment, commissioning and delivery to mine management and operation.

The Guinea 6,000t/d gold mineral processing plant was an EPC+M+O project. The design scope covered construction drawings and workshop drawings and involved engineers in the fields of mineral processing, water supply and drainage, power, civil engineering and general layout.

The Malaysia 700t/d gold mineral processing plant was a symbol of Chine-Malaysia cooperation in the mining industry under the policy of The Belt and Road. The raw ore consisted of pyrite, quartz, calcite and mica, with gold being the valuable mineral. It had a gold grade of 4.70g/t, silver grade of 4.63g/t, iron grade of 20.10% and a sulfur grade of 20.55%.

mineral processing caseguinea 6000tpd gold processing project-xinhai

mineral processing caseguinea 6000tpd gold processing project-xinhai

Xinhai mineral processing equipment mainly include: grinding equipment, flotation equipment, dewatering equipment, magnetic separation equipment, and so on. Some of the equipment is Xinhai independent research and development, and has been awarded national patent. View details

Gold CIP Production Line adsorbs gold from cyaniding pulp by active carbon including 7 steps: leaching pulp preparation, cyaniding leaching, carbon adsorption, gold loaded carbon desorption, pregnant solution electrodeposit, carbon acid regeneration, leaching pulp. View details

This is a country known as the geological miracle, who is rich in mineral resources and is an important resource-based country in West Africa. Guinea has a large variety of mineral resources, large reserves, wide distribution, high mining value and great development potential. In particular, bauxite, iron, gold, diamond, nickel, copper, cobalt and other resources occupy an important position in the world. In recent years, mining companies from around the world have been taking part in mining in guinea.

In 2018, Xinhai Mining formally signed the contract of 4000tpd gold processing plant with the client, providing it with one-stop and customized mineral processing EPC+M+O service. Xinhai Mining pointed out that due to the presence of gold particles, some gold particles were lost in the process of sampling, sample preparation and reduction in the original geological exploration process. Therefore, it is necessary to take large samples and then adopt gravity separation, and the concentrates, medium ores and tailings obtained by the gravity separation for sampling and analysis respectively, and the adhesion of gold particles on the equipment surface during the sample making process shall be considered.

The rigorous attitude, accurate data and customized services of Xinhai Mining were greatly appreciated by the client. And the client also recognized Xinhai Minings strong brand strength, customized mineral processing EPC+M+O service, advanced and reliable equipment quality and excellent customer service, which contributed to the partnership. Finally, Xinhai Mining only took 10 months (including 2 months of transportation and customs clearance) before the project was formally put into operation with considerable economic benefits.

In 2019, the client decided to expand the original 4000tpd gold processing plant and expand the production capacity to 6000tpd on the original basis. Based on the successful production practice in the first phase, the client chose Xinhai Mining for re-cooperation, and entrusted Xinhai Mining to provide one-stop, customized mineral processing EPC+M+O service for its 6000tpd gold processing project.

Ore Properties: the ore of this project was mainly oxidized ore, 80% of the ore was powdery clay ore, containing granular gold. The average grade of the ore was 1.0g/t, the quality of impurities is very little, the gold was the only recoverable element, and the ore was easy to be separated.

Most of the raw ore in this project was fine slime ore with fine particle size, which didnt need the crushing stage. The raw material can be directly fed to the raw material warehouse, or discharged to the raw material warehouse for storage, and then sent to the steel bin by the forklift truck. The material was fed into the belt conveyor by the belt feeder under the material bin, then sent to the ball mill for grinding.

The ore transported by the belt conveyor was sent to the ball mill for one stage grinding, the ore discharge of ball mill was sent to the jig by the slurry pump for gravity separation. The coarse concentrate obtained by the gravity separation of flowed automatically to the 6s shaking table for cleaning, the concentrate obtained by the shaking table flowed automatically to another 6s shaking table to get gold particles, the middlings and tailings obtained by the shaking table flowed automatically to the pump box, and then were pumped to the ball mill for grinding. The tailings of jig were sent to the cyclone unit by the slurry pump for one stage classification, the cyclone settling returned to the ball mill for re-grinding, the overflow flowed automatically to trash screen for removing impurity, and then was sent to two-stage hydrocyclone classification. The two-stage hydrocyclone (two groups of hydrocyclone) settling and part of the overflow was sent to leaching, other overflow flowed automatically to the thickener for enrichment.

The underflow density of the thickener was concentrated to about 40%, which was pumped into the double impeller efficient leaching tank by the slurry pump for leaching and carbon adsorption. And the roots fan was used to fill the leaching tank with air, the NaCN was added at the same time to make the full reaction among slurry, reagent and air.

The gold in ore reacted with NaCN in alkaline environment to form gold cyanogen complex ion. The gold entered the solution and was adsorbed by activated carbon. During the production, the carbon was extracted in reverse and the saturated gold-bearing carbon was extracted by the No.2 leaching tank. The undersize pulp was returned to the No.2 leaching tank. The oversize gold-bearing carbon was sent to the carbon storage tank for washing the carbon by the hydraulic conveying. The clean saturated gold-bearing carbon was re-sent to the desorption electrolysis system for gold processing, and the gold sludge was smelted in the high frequency melting furnace to obtain the final composite gold.

After a few times of use, the activity of activated carbon was weakened, the adsorption capacity of gold was decreased. In order to recover its activity and ensure its recycling, it is necessary to conduct regeneration treatment on degold-deoxidized carbon. There were two regeneration methods of activated carbon: one was pickling regeneration, another was high temperature activation regeneration.

The cyanide tailings were transported to the tailings pond by slurry pump for precipitation. The tailings were stocked in the pond, and the clarified water was returned to the production pond for recycling, so as to realize zero discharge of production sewage.

From mineral processing test, mine design, equipment manufacturing and procurement, packaging and delivery, installation and debugging, worker training, production standards reached to the project management and mine operation, all links were contracted by Xinhai Mining. The one-stop, customized plant solution was featured with high efficient project construction, short construction period, put into production quickly.

The price of concrete was expensive in Guinea, the cost of the same amount of concrete was about five times of China. In order to reduce the investment and speed up the construction speed, Xinhai Mining adopted combined steel structure (including the warehouse) for the above-ground part, the steel structure was totally pre-processed in China, which can be assembly, disassembly and movement flexibly after transported to the site with fast construction, low investment and beautiful shape.

80% of the ore were powdered clay ore, the raw ore contained 25%-30% water. On the one hand, Xinhai Mining solved the plugging and feeding problems of powdered clay.On the other hand, Xihai Mining adopted gravity separation + cyanide process, specially strengthened the gravity separation process and grinding process, that is, firstly recycled part of the gold particles in the gravity separation process, reduced the gold grade of entering the leaching operation, thereby reducing the reagent consumption, saving the production costs.

The whole plant was built according to terrain, each building was relatively concentrated. The equipment configuration in each plant room of the concentrator considers the main pulp to realize self-flow as far as possible.

the leaching agent used in the project adopted the environmentally friendly leaching agent with low toxicity, reagent consumption and cost. At the same time, the indicators obtained by this leaching agent is the same as the sodium cyanide.

At present, the Guinea 6000tpd gold processing plant project has been successfully put into operation, the whole plant operates steadily, the equipment quality is reliable, and the dressing index and economic benefits have reached the expectation. Xinhais professional mineral processing service strength has also been affirmed by the project customer.

The Guinea 6000tpd gold processing plant has successfully reached the standard and put into operation within a short time, which not only fully reflected the strong ore dressing strength, professional customized solutions and thoughtful customer service of Xinhai Mining, but also laid a solid foundation for further cooperation between the two sides.

After the successful operation of this gold processing plant, the project company in guinea quickly started the construction of another 15000tpd gold processing project in 2019, and continued to the cooperation with Xinhai Mining. At present, the Guinea 15000tpd gold processing plant has entered the stage of installation and debugging.

From the first cooperation, to the second cooperation, and then to the third cooperation, this project customer has become a partner who has a deep partnership with us. The mineral processing plants undertaken by Xinhai Mining has become the model project examples in local.

In Africa, more than 100 mineral processing EPC+M+O projects undertaken by Xinhai Mining spread in Guinea, Tanzania, Zimbabwe, Sudan, Nigeria, Morocco and other countries, effectively promoting the development of African mining industry. In the future, we will continue to adhere to the comprehensive deepening of reform, in-depth promotion of Xinhai solution, spread the correct concept and method of mine construction, and effectively provide global customers with more perfect, professional mineral processing EPC+M+O service!

ball mill, grinding mill, ball mill manufacturers, ball mill working principle - xinhai

ball mill, grinding mill, ball mill manufacturers, ball mill working principle - xinhai

Xinhai grinding mill has excellent energy saving ability. According to the customer demand, manganese steel liner and wear-resistant rubber liner can be customized for Xinhai ball mill with good wear resistance, long service life, easy maintenance

High-quality equipment manufacturing capabilities, focusing on the research and development and innovation of mineral processing equipment, extending the stable operation time of the equipment, and providing cost-effective services.

news - xinhai

news - xinhai

Usually, the maintenance and overhaul work of the flotation cell shall be equipped with full-time personnel, mainly including daily inspection, cleaning, lubrication and regular maintenance and other operations, so as to ensure the stable and continuous operation of the flotation cell.

Based on the above problems, the gold tailings disposal methods and comprehensive utilization of gold tailings is extremely urgent. At present, the common gold tailings disposal methods and comprehensive utilization mainly include the following ways: gold tailings reprocessing method, gold tailings dry stacking method, production of building materials, mine filling, reclamation and making field.

On March 18, The ceremony of Xinhai donating 250,000yuan scholarship to School of Chemistry and Biological in Shandong University of Science and Technology was held in meeting room of School of Chemistry and Biological.

On January 18th, Xinhai Mining EPC organized the 2020 Safety Summary Meeting and 2021 Safety Production Kick-off Meeting. Mr. Zhang Yunlong, chairman of Xinhai Mining, Mr. Han Qingwang, director of administration and operation, and the heads of various departments of the Production Management Center attended this meeting.

At the end of 2020, 84 teachers and students from the School of Chemical Engineering of Shandong University of Science and Technology came to Xinhai Mining for a 3-day visit and practice. Mr. Zhang Yunlong, chairman of Xinhai Mining EPC., and various departments warmly received the teachers and students and arranged a rich and reasonable internship program for them.

Time engraves new rings and records the footprints that go ahead. In the extraordinary 2020, we faced difficulties, turned against the wind, and became more brave as we fought. The hardworking and brave people in Xinhai, still handed over a shining performance report.

In recent years, "Green Mining" has become an inevitable choice for mining enterprises. As the "waste" after mineral processing, tailings has been recognized as the potential secondary resource, but traditional tailings wet discharging violates the principle "Green Mining".

Grinding mill has an impact on grinding cost and performance. The common grinding mills used in the mineral processing include ball mill machine, rod mill, autogenous mill, Raymond mill. Making a reasonable choice of grinding mill, reducing the grinding cost are important ways to improve the mineral processing efficiency.

Under the new situation, Xinhai Mining has paid long-term attention to extraction of gold, technology and equipment research & development. According to the different types of gold ore characteristics and user requirements, Xinhai has formed three kinds of gold mining processes for the extraction of gold, include gold cyanide leaching process, gold floatation process, gold gravity separation process.

According to the different grinding conditions, the ball mill can be divided into wet ball mill and dry ball mill. Before selecting the type of ball mill, we should know about the difference between the wet ball mill and dry ball mill, then make a targeted choice.

xinhai quality management systemserve clients with high quality, hold tight on quality management-xinhai

xinhai quality management systemserve clients with high quality, hold tight on quality management-xinhai

Xinhai mineral processing equipment mainly include: grinding equipment, flotation equipment, dewatering equipment, magnetic separation equipment, and so on. Some of the equipment is Xinhai independent research and development, and has been awarded national patent. View details

Gold CIP Production Line adsorbs gold from cyaniding pulp by active carbon including 7 steps: leaching pulp preparation, cyaniding leaching, carbon adsorption, gold loaded carbon desorption, pregnant solution electrodeposit, carbon acid regeneration, leaching pulp. View details

Quality is the core of enterprise development. In over 20 years, Xinhai keeps on exploring the way of high-quality service, user-centric and innovative. To provide high-quality service and product to clients, Xinhai set up a complete quality management system, trying to satisfy and exceed the hope of clients.

Xinhai sets quality management department, which is responsible for the quality inspection. The principal of quality management organize inspection once a week, to eliminate the all the problems at the beginning, and to inpel all the links strictly observing laws, standards, and specifications. Therefore, the effective self-regulation can be carried out. The team leaders of every projects organize meetings every day, analyzing the problems recording in checks and feeding back to the quality management department for solving together. Devoting to find problems and solve them at any times.

Since the raw material storage to production finishing, Xinhai has infiltrated product quality into all aspects of it. In production, Xinhai strictly follows the self-inspection, mutual inspection and other procedures for production. After production is completed, the equipment will also cooperate with the quality management department to carry put various inspections of the equipment.

Xinhai selected all kinds of raw materials according to Technical Standards for Raw Materials and Purchased Parts, Incoming Inspection And Test Control Procedures, Physical And Chemical Inspection Regulations, National Standard and other regulations. Xinhai has strict standards on flange, cylinder and other materials, and carrying out incoming inspection. Using full inspection or random inspection to prevent nonconforming material from entering.

The machining should be strictly according to the drawings and technology requirements. Ensure that the dimensional tolerance, geometric tolerance and smoothness of the workpiece meet the requirements. Before (after) processing, self-inspection and inspection must be carried out to avoid the production of large quantities of waste products.

During the production of equipment, the docking of materials must met the requirements of the drawings. Do not lead arcs on the material or deform the raw materials. Butt welds must not exceed the specified length. At the same time, the surface rust, iron slag and other debris must be treated, burrs, flashes, nozzles on the surface of the casting, etc. Components to ensure the aesthetics of the parts, and repair and polish the defective parts.

Welded equipment parts need to be checked for the presence of pores, slag inclusions, or large areas of splashes and cracks, to ensure that the welding size of the equipment does not exceed the scope of the drawings, and there are no under-welds, pits, cracks, or unwelded after welding forming, not-fused, etc.

According to GB8923-88 standard, the equipment parts is accepted. Keeping the steel surface clean, and ensure that the surface of the sprayed or projected rust-removing steel surface should be free of visible grease, dirt, scale, rust, paint coating and other attachments, and presenting a uniform metal color.

If the equipment passed the inspection, Xinhai Mining will issue a self-inspection report in compliance with the regulations. While reassuring customers, it is convenient for customer to conduct acceptance.

During the installation and construction, Xinhai Mining signed a project quality target pre-control letter with the project party, and the project party signed quality control agreements with each team of the installation team. The internal reward and punishment system was adopted to ensure the quality of the project by economic means. During installation and commissioning, the installation and debugging personnel will carefully compile the installation technical standards, installation inspection forms and installation plans of each equipment, use the materials according to the specifications in the drawings, and install and commission the team to conduct self-inspection after the installation project is completed, and then be reviewed by the quality inspector and then inspected by the owner, And ensure that all records of visas are kept complete and complete.

Xinhai Mining provides warranty service for products, and provide replacement parts for warranty products. If there are installation defect, Xinhai can send personnel to repair. Besides, Xinhai is equipped with dedicated online customers service and aftersale service department.

At present, Xinhai has passed ISO9001:2015 quality management system certification, EU CE certification, and other certifications. During the epidemic, while strengthening the epidemic prevention measures, Xinhai Mining Co., Ltd. overcomes difficulties and maintains the service quality of various projects at home and abroad. Many projects were successfully delivered during the epidemic, entered the installation and commissioning phase, and even successfully completed the commissioning work.

Till now, XInhai has completed over 500 mineral processing EPC+M+O projects, in over 90 countries and regions, and able to provide solutions for over 70 kinds of minerals. With the joint efforts of all Xinhai people, Xinhai Mining will always implement What you need is what we can do, continue to improve and innovate, and provide customers with high-quality products and services!

gold ball mill - xinhai

gold ball mill - xinhai

The steel ball is the grinding media of the gold ball mill. In the working process, the steel ball will directly affect the grinding efficiency of the gold ball mill and even the working efficiency and product quality of the whole concentrator.

Below, we will introduce the steel ball in detail from its specification and quantity, material, ratio and grading to help you choose and add the steel ball correctly, so as to improve the grinding efficiency of the gold ball mill.

Generally, the diameter of the steel ball is between 20mm and 125mm. Among them, the diameter of the small steel ball is generally 40mm and a 60mm, the diameter of the medium steel ball is generally 80mm, and the diameter of the large steel ball is 100mm or 120mm. The diameter of the super large steel ball is 130mm-150mm.

Theoretically, when the filling amount of steel ball in the ball mill is 40%, the ball mill can obtain the ideal output. But in the actual production, the filling rate of the steel ball in the ball mill is mostly about 35%, that is, the volume of the steel ball in the gold ball mill is kept slightly below the horizontal centerline of the ball mill.

As the "consumable" in the grinding operation, the wear degree of the steel ball is different due to the different material. At present, the mainstream steel balls of the gold ball mill on the market mainly include casting steel balls and forged steel balls.

Casting steel balls are mainly low chromium casting steel ball, medium chromium casting steel ball and high chromium casting steel ball, whose hardness, impact value and breakage rate are related to the metallographic structure of steel. The higher the chromium content, the better the wear resistance of the steel ball.

Forged steel gold ball mills mainly include low carbon alloy steel ball, medium carbon alloy steel ball, high manganese steel ball, rare earth chromium molybdenum alloy steel ball. The impact toughness of the forged steel ball is large, not easy to deform, but the crushing rate is low.

When first enabled, the gold ball mill needs the large, medium and small steel ball for matching, and the steel mill ball for the first time should be added to 80% of the amount limit that the ball mill manufacturer of ball mill suggests. Because the gears of the ball mill need mesh after the installation, and the processing capacity of the ball mill is increased gradually, then the ball mill operator needs to observe the condition of gear meshing in two or three days. If all is going well, the ball mill operator can open the hole cover to add the remaining 20% of steel ball.

Usually, the small steel balls are used only in the first addition. When the ball mill is running normally, there will be reasonable friction between the steel ball and the steel ball, the steel ball and the ore, the steel ball and the lining plate of the ball mill, which makes the wear increase. The large steel ball is ground into small, and the medium steel ball is ground into the small steel ball, so there is no need to add the small steel ball under normal circumstances. However, if the particle size of the useful mineral does not realize the monomer separation, and the grinding fineness of the ball mill cannot meet the separation requirements (especially the flotation separation requirements), the appropriate amount of small steel balls can be added into the gold ball mill.

In addition, the ball mill steel ball is constantly worn in the operation, the ball mill operator must regularly make up the steel ball and maintain the load filling rate of the steel ball and reasonable ratio.

Determine the grading scheme of the steel ball usually starts from the first warehouse (namely the coarse crushing warehouse). For the multi-bin ball mill, the grading of the first bin is particularly important. According to the cross-gradation principle, the minimum diameter of the steel ball in the previous bin determines the maximum diameter of the steel ball in the next bin. It can be seen that the grading of the steel ball in the first warehouse actually dominates the grading of the steel ball in the other warehouses.

The upper limit of the ball diameter is determined according to the upper limit of particle size of the grinding material. The average diameter of the steel ball is determined according to the average particle size of the grinding material.

The composition proportion of each specification steel ball is set according to the proportioned principle of "small at both ends and large in the middle" for the grinding body and the distribution characteristics of material size,.

Calculate the average ball diameter of the mixed steel ball, and compare with the original average ball diameter of the steel ball, add the steel ball according to the proportion of the ball size. If the deviation is large, it is necessary to set the composition proportion of various steel balls and rematch the balls until the deviation is small.

The secondary grading method means to only select two different diameters of ball mill steel balls for grading. The diameter of the large steel ball depends on the particle size of the grinding material, and the diameter of the small steel ball depends on the size of the space between the large steel balls.

Usually, the diameter of small steel ball should be 13%-33% of the diameter of large steel ball. Generally, the small steel ball accounted for 3%-5% of the mass of large steel ball, and the incorporation amount of small steel ball shouldnt affect the filling rate of large steel ball in principle.

These are the main aspects of the steel ball involved in the grinding process: specifications and quantity, material, ratio and grading. For the concentrator, the selection and application of the steel ball involve many technical problems, it is suggested that the mine owners carefully analyze their own actual situation, determine the suitable steel ball for the concentrator through consulting the professional gold ball mill manufacturers, thus avoiding the unnecessary economic losses.

ball milling - an overview | sciencedirect topics

ball milling - an overview | sciencedirect topics

Ball milling is often used not only for grinding powders but also for oxides or nanocomposite synthesis and/or structure/phase composition optimization [14,41]. Mechanical activation by ball milling is known to increase the material reactivity and uniformity of spatial distribution of elements [63]. Thus, postsynthesis processing of the materials by ball milling can help with the problem of minor admixture forming during cooling under air after high-temperature sintering due to phase instability.

Ball milling technique, using mechanical alloying and mechanical milling approaches were proposed to the word wide in the 8th decade of the last century for preparing a wide spectrum of powder materials and their alloys. In fact, ball milling process is not new and dates back to more than 150 years. It has been used in size comminutions of ore, mineral dressing, preparing talc powders and many other applications. It might be interesting for us to have a look at the history and development of ball milling and the corresponding products. The photo shows the STEM-BF image of a Cu-based alloy nanoparticle prepared by mechanical alloying (After El-Eskandarany, unpublished work, 2014).

Ball milling, a shear-force dominant process where the particle size goes on reducing by impact and attrition mainly consists of metallic balls (generally Zirconia (ZrO2) or steel balls), acting as grinding media and rotating shell to create centrifugal force. In this process, graphite (precursor) was breakdown by randomly striking with grinding media in the rotating shell to create shear and compression force which helps to overcome the weak Vander Waal's interaction between the graphite layers and results in their splintering. Fig. 4A schematic illustrates ball milling process for graphene preparation. Initially, because of large size of graphite, compressive force dominates and as the graphite gets fragmented, shear force cleaves graphite to produce graphene. However, excessive compression force may damage the crystalline properties of graphene and hence needs to be minimized by controlling the milling parameters e.g. milling duration, milling revolution per minute (rpm), ball-to-graphite/powder ratio (B/P), initial graphite weight, ball diameter. High quality graphene can be achieved under low milling speed; though it will increase the processing time which is highly undesirable for large scale production.

Fig. 4. (A) Schematic illustration of graphene preparation via ball milling. SEM images of bulk graphite (B), GSs/E-H (C) GSs/K (D); (E) and (F) are the respective TEM images; (G) Raman spectra of bulk graphite versus GSs exfoliated via wet milling in E-H and K.

Milling of graphite layers can be instigated in two states: (i) dry ball milling (DBM) and (ii) wet ball milling (WBM). WBM process requires surfactant/solvent such as N,N Dimethylformamide (DMF) [22], N-methylpyrrolidone (NMP) [26], deionized (DI) water [27], potassium acetate [28], 2-ethylhexanol (E-H) [29] and kerosene (K) [29] etc. and is comparatively simpler as compared with DBM. Fig. 4BD show the scanning electron microscopy (SEM) images of bulk graphite, graphene sheets (GSs) prepared in E-H (GSs/E-H) and K (GSs/K), respectively; the corresponding transmission electron microscopy (TEM) images and the Raman spectra are shown in Fig. 4EG, respectively [29].

Compared to this, DBM requires several milling agents e.g. sodium chloride (NaCl) [30], Melamine (Na2SO4) [31,32] etc., along with the metal balls to reduce the stress induced in graphite microstructures, and hence require additional purification for exfoliant's removal. Na2SO4 can be easily washed away by hot water [19] while ammonia-borane (NH3BH3), another exfoliant used to weaken the Vander Waal's bonding between graphite layers can be using ethanol [33]. Table 1 list few ball milling processes carried out using various milling agent (in case of DBM) and solvents (WBM) under different milling conditions.

Ball milling of graphite with appropriate stabilizers is another mode of exfoliation in liquid phase.21 Graphite is ground under high sheer rates with millimeter-sized metal balls causing exfoliation to graphene (Fig. 2.5), under wet or dry conditions. For instance, this method can be employed to produce nearly 50g of graphene in the absence of any oxidant.22 Graphite (50g) was ground in the ball mill with oxalic acid (20g) in this method for 20 hours, but, the separation of unexfoliated fraction was not discussed.22 Similarly, solvent-free graphite exfoliations were carried out under dry milling conditions using KOH,23 ammonia borane,24 and so on. The list of graphite exfoliations performed using ball milling is given in Table 2.2. However, the metallic impurities from the machinery used for ball milling are a major disadvantage of this method for certain applications.25

Reactive ball-milling (RBM) technique has been considered as a powerful tool for fabrication of metallic nitrides and hydrides via room temperature ball milling. The flowchart shows the mechanism of gas-solid reaction through RBM that was proposed by El-Eskandarany. In his model, the starting metallic powders are subjected to dramatic shear and impact forces that are generated by the ball-milling media. The powders are, therefore, disintegrated into smaller particles, and very clean or fresh oxygen-free active surfaces of the powders are created. The reactive milling atmosphere (nitrogen or hydrogen gases) was gettered and absorbed completely by the first atomically clean surfaces of the metallic ball-milled powders to react in a same manner as a gas-solid reaction owing to the mechanically induced reactive milling.

Ball milling is a grinding method that grinds nanotubes into extremely fine powders. During the ball milling process, the collision between the tiny rigid balls in a concealed container will generate localized high pressure. Usually, ceramic, flint pebbles and stainless steel are used.25 In order to further improve the quality of dispersion and introduce functional groups onto the nanotube surface, selected chemicals can be included in the container during the process. The factors that affect the quality of dispersion include the milling time, rotational speed, size of balls and balls/ nanotube amount ratio. Under certain processing conditions, the particles can be ground to as small as 100nm. This process has been employed to transform carbon nanotubes into smaller nanoparticles, to generate highly curved or closed shell carbon nanostructures from graphite, to enhance the saturation of lithium composition in SWCNTs, to modify the morphologies of cup-stacked carbon nanotubes and to generate different carbon nanoparticles from graphitic carbon for hydrogen storage application.25 Even though ball milling is easy to operate and suitable for powder polymers or monomers, process-induced damage on the nanotubes can occur.

Ball milling is a way to exfoliate graphite using lateral force, as opposed to the Scotch Tape or sonication that mainly use normal force. Ball mills, like the three roll machine, are a common occurrence in industry, for the production of fine particles. During the ball milling process, there are two factors that contribute to the exfoliation. The main factor contributing is the shear force applied by the balls. Using only shear force, one can produce large graphene flakes. The secondary factor is the collisions that occur during milling. Harsh collisions can break these large flakes and can potentially disrupt the crystal structure resulting in a more amorphous mass. So in order to create good-quality, high-area graphene, the collisions have to be minimized.

The ball-milling process is common in grinding machines as well as in reactors where various functional materials can be created by mechanochemical synthesis. A simple milling process reduces both CO2 generation and energy consumption during materials production. Herein a novel mechanochemical approach 1-3) to produce sophisticated carbon nanomaterials is reported. It is demonstrated that unique carbon nanostructures including carbon nanotubes and carbon onions are synthesized by high-speed ball-milling of steel balls. It is considered that the gas-phase reaction takes place around the surface of steel balls under local high temperatures induced by the collision-friction energy in ball-milling process, which results in phase separated unique carbon nanomaterials.

Conventional ball milling is a traditional powder-processing technique, which is mainly used for reducing particle sizes and for the mixing of different materials. The technique is widely used in mineral, pharmaceutical, and ceramic industries, as well as scientific laboratories. The HEBM technique discussed in this chapter is a new technique developed initially for producing new metastable materials, which cannot be produced using thermal equilibrium processes, and thus is very different from conventional ball milling technique. HEBM was first reported by Benjamin [38] in the 1960s. So far, a large range of new materials has been synthesized using HEBM. For example, oxide-dispersion-strengthened alloys are synthesized using a powerful high-energy ball mill (attritor) because conventional ball mills could not provide sufficient grinding energy [38]. Intensive research in the synthesis of new metastable materials by HEBM was stimulated by the pioneering work in the amorphization of the Ni-Nb alloys conducted by Kock et al. in 1983 [39]. Since then, a wide spectrum of metastable materials has been produced, including nanocrystalline [40], nanocomposite [41], nanoporous phases [42], supersaturated solid solutions [43], and amorphous alloys [44]. These new phase transformations induced by HEBM are generally referred as mechanical alloying (MA). At the same time, it was found that at room temperature, HEBM can activate chemical reactions which are normally only possible at high temperatures [45]. This is called reactive milling or mechano-chemistry. Reactive ball milling has produced a large range of nanosized oxides [46], nitrides [47], hydrides [48], and carbide [49] particles.

The major differences between conventional ball milling and the HEBM are listed in the Table 1. The impact energy of HEBM is typically 1000 times higher than the conventional ball milling energy. The dominant events in the conventional ball milling are particle fracturing and size reductions, which correspond to, actually, only the first stage of the HEBM. A longer milling time is therefore generally required for HEBM. In addition to milling energy, the controls of milling atmosphere and temperature are crucial in order to create the desired structural changes or chemical reactions. This table shows that HEBM can cover most work normally performed by conventional ball milling, however, conventional ball milling equipment cannot be used to conduct any HEBM work.

Different types of high-energy ball mills have been developed, including the Spex vibrating mill, planetary ball mill, high-energy rotating mill, and attritors [50]. In the nanotube synthesis, two types of HEBM mills have been used: a vibrating ball mill and a rotating ball mill. The vibrating-frame grinder (Pulverisette O, Fritsch) is shown in Fig. 1a. This mill uses only one large ball (diameter of 50 mm) and the media of the ball and vial can be stainless steel or ceramic tungsten carbide (WC). The milling chamber, as illustrated in Fig. 1b, is sealed with an O-ring so that the atmosphere can be changed via a valve. The pressure is monitored with an attached gauge during milling.

where Mb is the mass of the milling ball, Vmax the maximum velocity of the vial,/the impact frequency, and Mp the mass of powder. The milling intensity is a very important parameter to MA and reactive ball milling. For example, a full amorphization of a crystalline NiZr alloy can only be achieved with a milling intensity above an intensity threshold of 510 ms2 [52]. The amorphization process during ball milling can be seen from the images of transmission electron microscopy (TEM) in Fig. 2a, which were taken from samples milled for different lengths of time. The TEM images show that the size and number of NiZr crystals decrease with increasing milling time, and a full amorphization is achieved after milling for 165 h. The corresponding diffraction patterns in Fig. 2b confirm this gradual amorphization process. However, when milling below the intensity threshold, a mixture of nanocrystalline and amorphous phases is produced. This intensity threshold depends on milling temperature and alloy composition [52].

Figure 2. (a) Dark-field TEM image of Ni10Zr7 alloy milled for 0.5, 23, 73, and 165 h in the vibrating ball mill with a milling intensity of 940 ms2. (b) Corresponding electron diffraction patterns [52].

Fig. 3 shows a rotating steel mill and a schematic representation of milling action inside the milling chamber. The mill has a rotating horizontal cell loaded with several hardened steel balls. As the cell rotates, the balls drop onto the powder that is being ground. An external magnet is placed close to the cell to increase milling energy [53]. Different milling actions and intensities can be realized by adjusting the cell rotation rate and magnet position.

The atmosphere inside the chamber can be controlled, and adequate gas has to be selected for different milling experiments. For example, during the ball milling of pure Zr powder in the atmosphere of ammonia (NH3), a series of chemical reactions occur between Zr and NH3 [54,55]. The X-ray diffraction (XRD) patterns in Fig. 4 show the following reaction sequence as a function of milling time:

The mechanism of a HEBM process is quite complicated. During the HEBM, material particles are repeatedly flattened, fractured, and welded. Every time two steel balls collide or one ball hits the chamber wall, they trap some particles between their surfaces. Such high-energy impacts severely deform the particles and create atomically fresh, new surfaces, as well as a high density of dislocations and other structural defects [44]. A high defect density induced by HEBM can accelerate the diffusion process [56]. Alternatively, the deformation and fracturing of particles causes continuous size reduction and can lead to reduction in diffusion distances. This can at least reduce the reaction temperatures significantly, even if the reactions do not occur at room temperature [57,58]. Since newly created surfaces are most often very reactive and readily oxidize in air, the HEBM has to be conducted in an inert atmosphere. It is now recognized that the HEBM, along with other non-equilibrium techniques such as rapid quenching, irradiation/ion-implantation, plasma processing, and gas deposition, can produce a series of metastable and nanostructured materials, which are usually difficult to prepare using melting or conventional powder metallurgy methods [59,60]. In the next section, detailed structural and morphological changes of graphite during HEBM will be presented.

Ball milling and ultrasonication were used to reduce the particle size and distribution. During ball milling the weight (grams) ratio of balls-to-clay particles was 100:2.5 and the milling operation was run for 24 hours. The effect of different types of balls on particle size reduction and narrowing particle size distribution was studied. The milled particles were dispersed in xylene to disaggregate the clumps. Again, ultrasonication was done on milled samples in xylene. An investigation on the amplitude (80% and 90%), pulsation rate (5 s on and 5 s off, 8 s on and 4 s off) and time (15 min, 1 h and 4 h) of the ultrasonication process was done with respect to particle size distribution and the optimum conditions in our laboratory were determined. A particle size analyzer was used to characterize the nanoparticles based on the principles of laser diffraction and morphological studies.

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