hazards due to gold ball milling and gold thickeners

gold cyanide leaching process - xinhai

As a precious metal resource, the gold resources are gradually decreasing, the high-grade gold mining has come to an end, and the refractory gold and the associated gold in other minerals have become the focus of gold mining and recovery. At present, the most common gold extraction method for this kind of gold mine is the gold cyanide leaching process. But do you know the factors affecting gold leaching in cyanide leaching process?

In the mineral processing tests for refractory gold ores, the mineral processing test personnel usually selects variables to test, such as grinding fineness, pulp pH value, pulp temperature, agitating speed, cyanide agent dosage, pulp density, leaching time, and inflating volume. The above variables are the major factors affecting gold ore leaching. In addition, there are other factors affecting gold ore leaching, such as associated impurities in ore, amount of leaching aid, etc., which are various due to the ore differences, so they are not discussed here. Then, we will explore the impact of the above factors on gold leaching.

Generally speaking, the determination of grinding fineness is related to the ore dissemination characteristics. The grinding fineness is affected by the different ore dissemination characteristics, the size and morphology of gold particles.

Taking a gold mine as an example, the gold particle size of the gold mine is fine. The part of 0.037-0.01mm accounted for 56.32%, and that of less than 0.01mm accounted for 36.80%, which was embedded in various minerals as the intergranular condition.

The reason why the pH value of pulp, pulp temperature and agitating speed affect gold leaching is that cyanide is easy to generate hydrocyanic acid (HCN) through the reaction in the pulp. Hydrocyanic acid is volatile and toxic. If hydrocyanic acid volatiles from the pulp, it will cause cyanide loss and environmental pollution.

Therefore, in the gold cyanide leaching process, the pH value of the pulp is generally adjusted to 10-11, and the pulp temperature maintains an appropriate value (usually less than 15 ), and keeping uniform agitating, which can prevent the volatilization of hydrocyanic acid.

Gold is a kind of inactive metal, which can cause complexation reaction with cyanogen (CN-) under the action of oxygen in the cyanide leaching process, and then results in Au (CN) 2-. Therefore, cyanide agent dosage is one of the key factors determining the gold dissolution.

In general, the pulp should contain a certain amount of unbonded cyanogen, then the gold cyanide leaching can keep normal. And the specific dosage of cyanide agent should be determined according to the property of gold ore.

The slurry solid-liquid ratio is the pulp density, which can directly affect the diffusion rate of components, and then affect the gold leaching rate and speed. It is suggested to determine the appropriate pulp density through the mineral processing test.

When the pulp density is too low, the gold leaching speed and rate are improved, but the requirements on equipment volume are increased. So, the equipment investment cost is significantly increased, and the amount of cyanide agent will be increased correspondingly.

Gold cyanide leaching is a relatively slow process, the leaching time is over 24 hours generally, and the gold leaching rate is improved with the extension of leaching time, but the gold leaching speed is reduced corresponding, and finally, the gold leaching rate tends to a limit value. At that time, even the leaching time is extended, the gold leaching rate of is not improved obviously.

Taking a low-grade oxidized gold ore containing carbon and arsenic as an example, the leaching test was carried out when the grinding fineness -0.074mm accounted for 95%, the pulp density was 33% and pH value was 12, the gold leaching rate kept 81.48% when the leaching time was 24 hours, 36 hours and 48 hours respectively.

The reason for gold leaching needs to be inflated is that effective oxidation is conducive to the gold dissolution, so appropriately inflating can improve the solubility of oxygen in ore pulp, thus improving the dissolution rate of gold. Usually, increasing the inflating volume can be finished by inflating or agitating the pulp.

In conclusion, we can change the above factors to improve the gold leaching rate in the cyanide leaching process for refractory gold ores. It is suggested that the mineral owners should entrust a qualified mineral processing testing institution to conduct the mineral processing test, and determine the appropriate gold leaching conditions through the mineral processing test results, so that the mineral processing plant can obtain the reasonable process indicators, and avoid the late recovery after the production, reduce the loss of the mineral processing plant.

ball mills | industry grinder for mineral processing - jxsc machine

Max Feeding size <25mm Discharge size0.075-0.4mm Typesoverflow ball mills, grate discharge ball mills Service 24hrs quotation, custom made parts, processing flow design & optimization, one year warranty, on-site installation.

Ball mill, also known as ball grinding machine, a well-known ore grinding machine, widely used in the mining, construction, aggregate application. JXSC start the ball mill business since 1985, supply globally service includes design, manufacturing, installation, and free operation training. Type according to the discharge type, overflow ball mill, grate discharge ball mill; according to the grinding conditions, wet milling, dry grinding; according to the ball mill media. Wet grinding gold, chrome, tin, coltan, tantalite, silica sand, lead, pebble, and the like mining application. Dry grinding cement, building stone, power, etc. Grinding media ball steel ball, manganese, chrome, ceramic ball, etc. Common steel ball sizes 40mm, 60mm, 80mm, 100mm, 120mm. Ball mill liner Natural rubber plate, manganese steel plate, 50-130mm custom thickness. Features 1. Effective grinding technology for diverse applications 2. Long life and minimum maintenance 3. Automatization 4. Working Continuously 5. Quality guarantee, safe operation, energy-saving. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, to reduce the ore particle into fine and superfine size. Ball mills grinding tasks can be done under dry or wet conditions. Get to know more details of rock crushers, ore grinders, contact us!

Ball mill parts feed, discharge, barrel, gear, motor, reducer, bearing, bearing seat, frame, liner plate, steel ball, etc. Contact our overseas office for buying ball mill components, wear parts, and your mine site visits. Ball mill working principle High energy ball milling is a type of powder grinding mill used to grind ores and other materials to 25 mesh or extremely fine powders, mainly used in the mineral processing industry, both in open or closed circuits. Ball milling is a grinding method that reduces the product into a controlled final grind and a uniform size, usually, the manganese, iron, steel balls or ceramic are used in the collision container. The ball milling process prepared by rod mill, sag mill (autogenous / semi autogenous grinding mill), jaw crusher, cone crusher, and other single or multistage crushing and screening. Ball mill manufacturer With more than 35 years of experience in grinding balls mill technology, JXSC design and produce heavy-duty scientific ball mill with long life minimum maintenance among industrial use, laboratory use. Besides, portable ball mills are designed for the mobile mineral processing plant. How much the ball mill, and how much invest a crushing plant? contact us today! Find more ball mill diagram at ball mill PDF ServiceBall mill design, Testing of the material, grinding circuit design, on site installation. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, get to know more details of rock crushers, ore grinders, contact us! sag mill vs ball mill, rod mill vs ball mill

How many types of ball mill 1. Based on the axial orientation a. Horizontal ball mill. It is the most common type supplied from ball mill manufacturers in China. Although the capacity, specification, and structure may vary from every supplier, they are basically shaped like a cylinder with a drum inside its chamber. As the name implies, it comes in a longer and thinner shape form that vertical ball mills. Most horizontal ball mills have timers that shut down automatically when the material is fully processed. b. Vertical ball mills are not very commonly used in industries owing to its capacity limitation and specific structure. Vertical roller mill comes in the form of an erect cylinder rather than a horizontal type like a detachable drum, that is the vertical grinding mill only produced base on custom requirements by vertical ball mill manufacturers. 2. Base on the loading capacity Ball mill manufacturers in China design different ball mill sizes to meet the customers from various sectors of the public administration, such as colleges and universities, metallurgical institutes, and mines. a. Industrial ball mills. They are applied in the manufacturing factories, where they need them to grind a huge amount of material into specific particles, and alway interlink with other equipment like feeder, vibrating screen. Such as ball mill for mining, ceramic industry, cement grinding. b. Planetary Ball Mills, small ball mill. They are intended for usage in the testing laboratory, usually come in the form of vertical structure, has a small chamber and small loading capacity. Ball mill for sale In all the ore mining beneficiation and concentrating processes, including gravity separation, chemical, froth flotation, the working principle is to prepare fine size ores by crushing and grinding often with rock crushers, rod mill, and ball mils for the subsequent treatment. Over a period of many years development, the fine grinding fineness have been reduced many times, and the ball mill machine has become the widest used grinding machine in various applications due to solid structure, and low operation cost. The ball miller machine is a tumbling mill that uses steel milling balls as the grinding media, applied in either primary grinding or secondary grinding applications. The feed can be dry or wet, as for dry materials process, the shell dustproof to minimize the dust pollution. Gear drive mill barrel tumbles iron or steel balls with the ore at a speed. Usually, the balls filling rate about 40%, the mill balls size are initially 3080 cm diameter but gradually wore away as the ore was ground. In general, ball mill grinder can be fed either wet or dry, the ball mill machine is classed by electric power rather than diameter and capacity. JXSC ball mill manufacturer has industrial ball mill and small ball mill for sale, power range 18.5-800KW. During the production process, the ball grinding machine may be called cement mill, limestone ball mill, sand mill, coal mill, pebble mill, rotary ball mill, wet grinding mill, etc. JXSC ball mills are designed for high capacity long service, good quality match Metso ball mill. Grinding media Grinding balls for mining usually adopt wet grinding ball mills, mostly manganese, steel, lead balls. Ceramic balls for ball mill often seen in the laboratory. Types of ball mill: wet grinding ball mill, dry grinding ball mill, horizontal ball mill, vibration mill, large ball mill, coal mill, stone mill grinder, tumbling ball mill, etc. The ball mill barrel is filled with powder and milling media, the powder can reduce the balls falling impact, but if the power too much that may cause balls to stick to the container side. Along with the rotational force, the crushing action mill the power, so, it is essential to ensure that there is enough space for media to tumble effectively. How does ball mill work The material fed into the drum through the hopper, motor drive cylinder rotates, causing grinding balls rises and falls follow the drum rotation direction, the grinding media be lifted to a certain height and then fall back into the cylinder and onto the material to be ground. The rotation speed is a key point related to the ball mill efficiency, rotation speed too great or too small, neither bring good grinding result. Based on experience, the rotat

ion is usually set between 4-20/minute, if the speed too great, may create centrifuge force thus the grinding balls stay with the mill perimeter and dont fall. In summary, it depends on the mill diameter, the larger the diameter, the slower the rotation (the suitable rotation speed adjusted before delivery). What is critical speed of ball mill? The critical speed of the ball mill is the speed at which the centrifugal force is equal to the gravity on the inner surface of the mill so that no ball falls from its position onto the mill shell. Ball mill machines usually operates at 65-75% of critical speed. What is the ball mill price? There are many factors affects the ball mill cost, for quicker quotations, kindly let me know the following basic information. (1) Application, what is the grinding material? (2) required capacity, feeding and discharge size (3) dry or wet grinding (4) single machine or complete processing plant, etc.

gold leaching

This leach plant shows the continuous counter-current decantation system, in which all the ore is first reduced to a very fine state in the grinding mill-classifier circuit, in a Gold Leaching solution. The slime overflow of the classifier, usually 70%200 mesh, or finer, is sent to the first thickener, known as the primary thickener.

Here the pregnant solution, containing a large part of the dissolved gold and silver values, overflows from the top of the thickener and is sent to a clarifier, then to the precipitating system where the gold and silver values are precipitated, the precipitate periodically being reduced to bullion in a furnace.

The underflow pulp of the primary thickener, containing the remaining values and usually at a pulp ratio of 1:1, is elevated by a diaphragm pump into a series of agitators. The agitators are used to aid in the dissolution of the remaining values, augmented by the introduction of air. The time of treatment required depends upon the values still remaining in the slimes or fine sands in the mill pulps.

From the agitators, the pulp at a density of approximately 1:1 overflows directly into the first of a series of secondary thickeners. This feed pulp is diluted with the overflow solution from the second of the secondary thickeners, which solution has been enriched by the removal of values from the second and third secondary thickeners. After the solution is intimately mixed with the pulp it enters the thickener feed well, rises to the top of the thickener, is overflowed and is pumped to either the mill solution tank or introduced into the precipitation system. The thickened pulp from the first of the secondary thickeners settles to the bottom, is raked to the center discharge, and is then pumped to the second secondary thickener where it is mixed with the overflow solution from the third of the secondary thickeners. Thus the pulp flows in one direction with gradually decreasing values, while the solution is pumped in the opposite direction with gradually increasing values, from a barren wash water to a sufficiently enriched solution suitable for precipitation or mill solution storage.

This next gold leaching circuit is practically the same as Flowsheet No. CY-1, only in place of the last two secondary thickeners a rotary filter is used. On some ores two or more thickeners are used between the agitators and the filter. There is no question about the lower soluble loss when using a filter but the cost of the filter operation, amounting to from 8c to 10c per ton, is an important item as compared to the low cost of operating thickeners. Therefore, the question as to whether a filter or a thickener is to be used at the tail end of the Gold Leaching mill is a matter of economics, depending upon the housing facilities, initial investment in the plant, and operating cost. A tailing filter is necessary where water for milling is scarce, or where pollution of streams is prohibited.

That Leaching Process Circuit is shown one of theoutstanding improvements made in cyanidation whereby the coarse metallic minerals are removed from the grinding circuit by means of the Mineral Jig. The hutch product from this jig is amalgamated with a Amalgamator or CleanUp Pan and thus the coarse mineral values, such as metallic gold, are removed from the circuit before complete fine grinding takes place. This jig hutch product containing most of the fine as well as thecoarse metallics, can also be treated by a separate grinding and Leaching treatment plant.

By the early removal of the coarse gold and other minerals, it is possible to materially reduce the chemical consumption in the Gold Leaching plant and also the time required for agitation, as well as offering the possibility of grinding at a coarser mesh. In other words, the removal of a certain portion of the minerals at a coarse mesh, and their separate treatment, either by amalgamation or by a small Gold Leaching plant, eliminates the necessity of fine grinding the entire tonnage to recover the values from this small portion of the ore that often contains the majority of values.

The balance of the circuit is then similar to that shown on Flowsheet No. CY-1, with the advantages, however, of lower chemical consumption and a lower agitating time, with less equipment needed for final thickening and filtering. This is due to the high efficiency of the Mineral Jig in removing not only the coarse values that are free and that would require additional time and equipment, but also in removing most of the middling values that would require finer grinding of ore and higher costs.

This is similar to Leaching Process Circuit Flowsheet No. CY-3, excepting that a Unit Flotation Cell is used between the ball mill and the classifier to remove cyanicides or harmful elements from the Gold Leaching circuit, thus preventing an excessive chemical consumption. This concentrate produced on the Unit Flotation Cell can be sent to a smelter or treated separately from the balance of the Gold Leaching circuit. This method of treatment has been proved distinctly advantageous and should have an important application on ores where copper and other cyanicides are present. Flotation chemicals or reagents used in the Unit Flotation Cell do not affect the subsequent treatment by gold cyanidation.

In many instances this Unit Flotation Cell, due to the additional aeration secured, plays an important part in the chemical reaction between the cyanide and the gold and silver values. In the cyaniding of silver ores it is essential to have ample air and therefore the air that is introduced in the Unit Flotation Cell and in the Super-Agitators, is very important.

gold processing | britannica

For thousands of years the word gold has connoted something of beauty or value. These images are derived from two properties of gold, its colour and its chemical stability. The colour of gold is due to the electronic structure of the gold atom, which absorbs electromagnetic radiation with wavelengths less than 5600 angstroms but reflects wavelengths greater than 5600 angstromsthe wavelength of yellow light. Golds chemical stability is based on the relative instability of the compounds that it forms with oxygen and watera characteristic that allows gold to be refined from less noble metals by oxidizing the other metals and then separating them from the molten gold as a dross. However, gold is readily dissolved in a number of solvents, including oxidizing solutions of hydrochloric acid and dilute solutions of sodium cyanide. Gold readily dissolves in these solvents because of the formation of complex ions that are very stable.

Gold (Au) melts at a temperature of 1,064 C (1,947 F). Its relatively high density (19.3 grams per cubic centimetre) has made it amenable to recovery by placer mining and gravity concentration techniques. With a face-centred cubic crystal structure, it is characterized by a softness or malleability that lends itself to being shaped into intricate structures without sophisticated metalworking equipment. This in turn has led to its application, from earliest times, to the fabrication of jewelry and decorative items.

The history of gold extends back at least 6,000 years, the earliest identifiable, realistically dated finds having been made in Egypt and Mesopotamia c. 4000 bc. The earliest major find was located on the Bulgarian shores of the Black Sea near the present city of Varna. By 3000 bc gold rings were used as a method of payment. Until the time of Christ, Egypt remained the centre of gold production. Gold was, however, also found in India, Ireland, Gaul, and the Iberian Peninsula. With the exception of coinage, virtually all uses of the metal were decorativee.g., for weapons, goblets, jewelry, and statuary.

Egyptian wall reliefs from 2300 bc show gold in various stages of refining and mechanical working. During these ancient times, gold was mined from alluvial placersthat is, particles of elemental gold found in river sands. The gold was concentrated by washing away the lighter river sands with water, leaving behind the dense gold particles, which could then be further concentrated by melting. By 2000 bc the process of purifying gold-silver alloys with salt to remove the silver was developed. The mining of alluvial deposits and, later, lode or vein deposits required crushing prior to gold extraction, and this consumed immense amounts of manpower. By ad 100, up to 40,000 slaves were employed in gold mining in Spain. The advent of Christianity somewhat tempered the demand for gold until about the 10th century. The technique of amalgamation, alloying with mercury to improve the recovery of gold, was discovered at about this time.

The colonization of South and Central America that began during the 16th century resulted in the mining and refining of gold in the New World before its transferal to Europe; however, the American mines were a greater source of silver than gold. During the early to mid-18th century, large gold deposits were discovered in Brazil and on the eastern slopes of the Ural Mountains in Russia. Major alluvial deposits were found in Siberia in 1840, and gold was discovered in California in 1848. The largest gold find in history is in the Witwatersrand of South Africa. Discovered in 1886, it produced 25 percent of the worlds gold by 1899 and 40 percent by 1985. The discovery of the Witwatersrand deposit coincided with the discovery of the cyanidation process, which made it possible to recover gold values that had escaped both gravity concentration and amalgamation. With E.B. Millers process of refining impure gold with chlorine gas (patented in Britain in 1867) and Emil Wohlwills electrorefining process (introduced in Hamburg, Ger., in 1878), it became possible routinely to achieve higher purities than had been allowed by fire refining.

The major ores of gold contain gold in its native form and are both exogenetic (formed at the Earths surface) and endogenetic (formed within the Earth). The best-known of the exogenetic ores is alluvial gold. Alluvial gold refers to gold found in riverbeds, streambeds, and floodplains. It is invariably elemental gold and usually made up of very fine particles. Alluvial gold deposits are formed through the weathering actions of wind, rain, and temperature change on rocks containing gold. They were the type most commonly mined in antiquity. Exogenetic gold can also exist as oxidized ore bodies that have formed under a process called secondary enrichment, in which other metallic elements and sulfides are gradually leached away, leaving behind gold and insoluble oxide minerals as surface deposits.

Endogenetic gold ores include vein and lode deposits of elemental gold in quartzite or mixtures of quartzite and various iron sulfide minerals, particularly pyrite (FeS2) and pyrrhotite (Fe1-xS). When present in sulfide ore bodies, the gold, although still elemental in form, is so finely disseminated that concentration by methods such as those applied to alluvial gold is impossible.

Native gold is the most common mineral of gold, accounting for about 80 percent of the metal in the Earths crust. It occasionally is found as nuggets as large as 12 millimetres (0.5 inch) in diameter, and on rare occasions nuggets of native gold weighing up to 50 kilograms are foundthe largest having weighed 92 kilograms. Native gold invariably contains about 0.1 to 4 percent silver. Electrum is a gold-silver alloy containing 20 to 45 percent silver. It varies from pale yellow to silver white in colour and is usually associated with silver sulfide mineral deposits.

Gold also forms minerals with the element tellurium; the most common of these are calaverite (AuTe2) and sylvanite (AuAgTe4). Other minerals of gold are sufficiently rare as to have little economic significance.

Of the worlds known mineral reserves of gold ore, 50 percent is found in South Africa, and most of the rest is divided among Russia, Canada, Australia, Brazil, and the United States. The largest single gold ore body in the world is in the Witwatersrand of South Africa.