Mineral Processing Engineering

Thiocyanic Acid in Ion Exchange & Solvent Extraction of Metals

Metal separations and metal recoveries by ion exchange and solvent extraction of their thiocyanate complexes are widely practiced in analytical chemistry as well as in some industries. Consequently, a critical review of the chemistry of thiocyanic acid and thiocyanates is presented in the second part with the aim of providing a clearer understanding on the causes of these problems and giving options as how to minimize them.

Metal Thiocyanate Systems

Similar to hydrochloric acid, thiocyanic acid (a psudohalogenic acid) forms stable thiocyanato complexes with a large number of metals.

The liquid ion exchange reactions involved are given below.


The extraction efficiency follows the order Zn>Co>Cu>Fe>Mn>Ni.

Zn²+(a) + 2 SCN- (a) ↔ Zn(NCS)2(o)……………………………………………………………..(4)

This equation applies over the whole pH range for Zn(II) in the absence of any complexing anions. The extraction is quantitative and can be used in the preparation of pure zinc thiocyanate and in the separation of zinc and cadmium.

Thiocyanic Acid and Thiocyanates

Gaseous thiocyanic acid is readily soluble in water, alcohol and benzene. On cooling the gas to -30° to -40°C a white crystalline solid HNCS results, but it is difficult to obtain the pure white solid on account

By |2018-09-10T22:48:54+00:00September 10th, 2018|Categories: Hydrometallurgy|Tags: |Comments Off on Thiocyanic Acid in Ion Exchange & Solvent Extraction of Metals

Scaling Method for Modeling In Situ Leaching

The scaling technique significantly reduces computation time below that required for streamline modeling and simplifies desk-top calculations. The scaling technique applies to any flow processes (tracers, nonadsorbing species, or displacements) where chromatographic spreading/sharpening overrides physical dispersion.

Description of Streamline-Material Balance Model

In order to develop a standard for measuring the scaling technique, we present a brief description of the streamline-material balance model. Both restoration and leaching models are based on the coupling of streamlines with material balances.

The travel time T of a fluid particle along a streamline is


where Δtk is the travel time over a finite increment


and M is the total number of increments required for the streamline to traverse from injector to producer. Thus, the length of the streamline is

L = MΔl……………………………………………………………………….(3)

Since mobilities are constant, the flow rate associated with each streamline is constant and given as


where Qp is the production well flow rate and Ns is the number of streamlines associated with each producer. Since streamlines are traced backward, the production rate, instead of injection rate, is used in computing the streamline

By |2018-09-10T22:50:52+00:00September 10th, 2018|Categories: Leaching|Tags: |Comments Off on Scaling Method for Modeling In Situ Leaching

Sulfurous Acid Pre-Leaching – Manganese Silver Ore Treatment

The Tonopah silver mining district, was first discovered in the summer of 1900 and primitive small scale mining operations had started by the end of the year.

Millers Tailings Mineralogy

Mineralogical studies showed that the principal gangue minerals in the Millers tailings were, in order of abundance, quartz, feldspar and sericite. Hornblende, chlorite and a carbonate, possibly rhodocrosite, were also identified.

Chemical analysis of samples showed that, in addition to silver and gold, the Millers tailings contain 1.3-1.6% iron and 0.3-0.5% manganese. Other metals were present in insignificant quantities, viz., Copper – 0.01% or less, Zinc – 0.1% or less, Arsenic 0.05% or less, and Molybdenum, Tellumium, Mercury, Cadmium, Antimony all less than 0.001%. The samples showed variable organic content between 0.03% and 0.3%.

Development Test Work of the Sulfurous Acid Pre-Leach Process at Millers

Test work had shown that only 40-50% of the silver values could be leached by conventional cyanidation from the Tonopah Mining Company tailings, whereas upwards of 65% could be extracted from the Tonopah Belmont Development Company tailings.

Only minor improvements in silver extraction could be attained by increasingly fine grinding, additional cyanide addition and extension of the leach residence time. It was, however, shown that carbon-in-leach had

By |2018-09-10T22:53:21+00:00September 10th, 2018|Categories: Leaching|Tags: |Comments Off on Sulfurous Acid Pre-Leaching – Manganese Silver Ore Treatment

Steel Consumption in Open Circuit Grinding

The corrosion measurements were made using a corrater in pulp of concentrate and water agitated in a three-neck flask. The variables were to be percent solids, temperature, reducing reagent and pH. In the next step it was found that redissolution of oxygen after its removal was very rapid. The most effective reagents to prevent this action were sodium sulfide at elevated pH, sodium sulfite and sodium bisulfite in the order of importance. The next step of the study was to determine the effect of several variables on the effectiveness of these three reagents.

Experimental Procedures

The grinding balls were furnished by Sidbec-Normines Ltd, being minus 3,8 cm Norforge drop forged steel balls taken from a plant mill such that an equilibrium size may be assumed. A weight of 8,45 kg of balls occupied 2260 ml or 40% of the mill volume.

At the end of each test the load was quickly dumped on a 0,62 cm screen which retained the grinding balls. The latter were washed in place with a stream of water. Immediately after the water-wash the balls were immersed in a bath of methanol then quickly dried with absorbent paper to avoid corrosion of their surfaces.

The main dependent variable

By |2018-09-10T22:53:55+00:00September 10th, 2018|Categories: Grinding|Tags: |Comments Off on Steel Consumption in Open Circuit Grinding

Smelting & Refining Terms and Conditions – Typical Example

One of the most frequently asked questions is: “Where is copper (price and usage) going?” I will not attempt to forecast either the future price of copper or the future growth of the copper industry; rather I would like to discuss the current trends experienced in the smelting and refining terms and conditions for sales and/or purchases of copper concentrates.

A brief review of contract language and terms, together with a review of the common jargon, I believe, would be helpful. To accomplish this review, I will first list what I consider the four basic parts or sections of a basic ore contract and then illustrate basic terms with calculations.

Most ore contracts contain or refer to items in the following basic outline:

A) 1. Contracting Parties
2. Product
3. Quality
4. Quantity
5. Duration

B) 1. Delivery Basis (F.O.B., C.&F., C.I.F., etc.)
2. Shipping Schedule
3. Constructive Delivery

C) 1. Metal Payments and/or Return of Metal
2. Treatment and Refining and Delivery Deductions
3. Penalty Items

D) 1. Weighing, Sampling and Assaying
2. Settlement
3. Force Majeure
4. Diversion
5. Arbitration
6. Definitions
7. Specific Issues: Environmental Situations, Economic Stabilization, Duties, etc.

Many of the above items are self-explanatory and need no further discussion; others I will comment upon and advise what ideas or attitudes reflect recent trends.


By |2018-09-10T22:58:50+00:00September 9th, 2018|Categories: Smelting - Melting - Refining|Tags: |Comments Off on Smelting & Refining Terms and Conditions – Typical Example

Slurry Handling

The need to move large tonnages of slurry has grown as mines have become larger. As existing tailing depositories are filled up, new mines developed, or environmental requirements dictate, it becomes necessary to transport tailing particularly over longer distances.

There are two basic types of slurry transport systems, packed flow and slack flow. Packed flow is typified by a pipe running full; slack flow by a launder or pipe running less than full. Slack flow in launders or channels is also referred to as open channel flow. Generally slack flow slurry transportation involves a flow with less than 65 per cent solids, and there is an upper limit on particle size, depending on the slope of the system.

Today, however, flows and the required structures can be large and expensive, and a more reliable design procedure is necessary. Also, several conditions such as maximum, design, and minimum flow are often recognized and must be accommodated. It should be noted that a system may work well for a design or maximum flow, but may not function correctly for a minimum volume, sometimes as low as one third of the maximum.

slurry handling transport system

By |2018-09-10T22:55:33+00:00September 9th, 2018|Categories: Pumping & Conveying|Tags: |Comments Off on Slurry Handling

Platinum Palladium Ore Processing Flotation Pilot

We have been conducting research on methods for beneficiating platinum-palladium ores from the Stillwater Complex, Montana. The Stillwater Complex contains the only known major deposits of platinum-palladium ores in the 48 contiguous States. Exploration by Johns-Manville Corp. (Manville Corp.) has resulted in the delineation of an approximately stratigraphic zone (J-M Reef) rich in platinum- and palladium-bearing sulfide minerals. The zone is 1 to 3 m thick, is composed of anorthositic rocks, and has been traced for 40 km. Anaconda Minerals Co. has been exploring a platinum-palladium deposit which is the strike extension of the J-M Reef developed farther to the west. The extension, called the Howland Reef, is sheared and serpentinized, and there are significant differences in primary stratigraphy between the Howland Reef and the J-M Reef.

The Bureau has conducted flotation studies on the anorthositic ore from the complex but not on serpentinized ores. This report presents the results of a pilot mill study using xanthate-normal dodecyl mercaptan suites in the flotation of serpentinized ore from Anaconda’s Minneapolis Adit on the Rowland Reef.

Sample Description

A 20-ton bulk sample of minus 2-in ore from the Minneapolis Adit was obtained for pilot mill testing. Analysis of the sample showed 0.10 oz/ton

By |2018-09-08T07:16:12+00:00September 8th, 2018|Categories: Flotation|Tags: |Comments Off on Platinum Palladium Ore Processing Flotation Pilot

Rod Mill Grinding to Improve Gravity Recovery

The following discussion outlines the reasons behind and consequences of operating Cantung’s unusual rod mill/rod mill grinding circuit. Due emphasis has been placed on comparative analysis of the data available for the 1977-79 rod mill/ball mill period and the following 1980-82 period of rod mill/rod mill grinding circuit configuration. Conclusions are based on data relating mill feed grade, size distributions of table circuit feed with the resultant gravity concentrate recovery, and overall mill recovery.

Scheelite is more friable than other mineral constituents of the ore. Comparison of typical screen analyses of mill feed (primary rod mill feed) in Table 3 and Primary rod mill discharge in Table 4 illustrates the tendency of grinding to produce scheelite slimes. Gravity concentration of coarser scheelite yields a premium priced gravity product. Finer scheelite is recovered in the flotation concentrate. Scheelite in the minus 15 micron size fraction is difficult to recover by any method. Optimum grinding operation, then, involves the production of a closely sized material with a minimum of fines. The sensitivity of grinding and classification equipment has therefore been critically important to the operation of the Cantung mill.

In consideration of the above, it was decided, in the 1979 expansion, to incorporate a

By |2018-09-15T00:04:04+00:00September 8th, 2018|Categories: Gravity Concentration|Tags: |Comments Off on Rod Mill Grinding to Improve Gravity Recovery

Hydrocyclones for Cleaning Middlings

Due to a tight ash constraint on the clean coal product and difficult middlings washability characteristics, a considerable amount of coal was being lost in the jig middlings at the Monterey No, 2 Mine. A reverse two-stage hydrocyclone system cleaning at low specific gravities was selected. This system is currently recovering approximately 5.8 kg/s (23 tph) of 11.5% to 12.5% ash coal.

Process Selection

By searching the literature, consulting with equipment manufacturers and others in the coal industry, and evaluating our own ideas we accumulated a list of potential middlings processing methods for consideration. The list included (1) heavy media cyclones; (2) fine coal jigs or middlings jigs; (3) crush, screen and recirculate to existing jigs; and (4) two-stage hvdrocyclones connected in either conventional or reverse circuits.

Selecting between the reverse and conventional two-stage hydrocyclone circuits came down to product tonnage and quality, since all other factors were essentially equal. The tonnage and quality estimates for the two circuits were derived from theoretical distribution curves for the individual stages which were mathematically combined into a single distribution curve for each two-stage hydrocyclone circuit

The reverse circuit achieves a cleaner product because it rejects the high ash, heavier specific gravity fractions of the

By |2018-09-15T00:05:56+00:00September 8th, 2018|Categories: Classification|Tags: |Comments Off on Hydrocyclones for Cleaning Middlings

Gold Mill Tailings Restoration

Environmental Setting

A basic understanding of the climatic characteristics, geology, surface and groundwater hydrology conditions together with the physical and chemical characteristics of selected mill tailings deposits will aid in understanding the environmental problems associated with tailings disposal and restoration.

The Black Hills region is in the mid-latitudes which have a prevailing westernly airflow. The weather in this region is typical of a high elevation continental climate, characterized by extremes of summer heat (+100° F, +37.8 degrees Celsius) and winter cold (-30° F, -35.6 degrees Celsius) which are modified by the prominence of the mountainous uplifts. Winters are quite cold with near subfreezing temperatures normally occurring from December through March.

Physiographically, the Black Hills are located in a division of the Great Plains Province. The Black Hills are an elliptical uplift approximately 125 miles (201.2 km) long and 65 miles (104.6 km) wide. Rocks in the region range from Precambrian to Cretaceous. The metamorphic history and structure of the area are complex.

The Black Hills are within the Cheyenne River Basin, most of which is gently rolling plain. Watersheds in the Black Hills possess steep land slopes averaging 27 percent. These slopes are predominantly forested. Topographic conditions are characterized by high relief

By |2018-09-07T17:44:53+00:00September 7th, 2018|Categories: Environment & Tailings|Tags: |Comments Off on Gold Mill Tailings Restoration

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