Calcium Chloride Applications for the Mining Industry

Calcium Chloride Applications for the Mining Industry

There’s nothing very complicated about calcium chloride. It’s simply a material produced from natural brine deposits under the ground. It’s processed into a colorless, odorless liquid or into solid form as pure white flakes and pellets. CaCl₂ is its chemical symbol.

Four unique properties

Four properties of calcium chloride make this basic chemical compound a versatile material for the mining industry. The first three properties all relate to calcium chloride’s constant urge to return, or remain, in its natural liquid state.

1. Calcium chloride is deliquescent, meaning it’s able to absorb moisture from the air. It then holds onto the water for a long time, resisting evaporation. This property makes it ideal for controlling dust and, as a result, keeping road surfaces stable.
2. Once calcium chloride has absorbed all the moisture it can hold, it dissolves and spreads as it tries to return to a liquid. This is why relatively little calcium chloride is needed to control dust and melt snow and ice.
3. As calcium chloride dissolves, it gives off heat. Technically, it’s exothermic. Once completely dissolved in water, it can lower the solution’s freezing point to as low as -59°F (-50.6°C). This explains why it has long been used to melt snow and ice on haul roads, or anywhere else deicing is needed.
4. Lastly, a calcium chloride solution is a heavy fluid. Up to 30% heavier than water alone. This property combined with calcium chloride’s ability to greatly lower the freezing point of water illustrates one reason why it’s a useful, economical, year-round tire weighting material.

These unusual properties of calcium chloride combine to create a chain reaction of benefits everywhere the material is used. Calcium chloride is produced in three forms: liquid (LIQUIDOW 32, 35, and 38% liquid calcium chloride), pellet (PELADOW 94-97% calcium chloride) and flake (Dowflake Xtra 83-87% calcium chloride).

This [article] has been prepared to introduce you to the many uses of calcium chloride for mining applications, the benefits it provides and some insight into how calcium chloride should be used in each application.

Now that effective dust control in the mine has been made a requirement by the Federal Coal Mine Health and Safety Act, the problem facing mine officials is one of meeting the standards in the most economical way. Calcium chloride becomes valuable here, especially when it’s used to control dust on shuttle-car roadways. These paths create special problems as coal or ore and overburden is spilled and quickly pulverized. The fine dust is constantly stirred up and kept suspended in the air by the continuous traffic.

In this application, calcium chloride’s thirst for moisture enables it to keep those particles on the mine floor by keeping the surface slightly damp for long periods of time. Dust is controlled and clean air standards are more easily met.

Roadway stabilization is also achieved as an automatic byproduct of dust control. Dust particles kept on the roadway are left to add density and act as binder material. The roadway remains compacted, hard and smooth.

Application rates and methods

The amount of calcium chloride needed varies according to the dryness of the shuttle-car roadway. Initial applications are generally recommended at a rate of 1.65 lbs. of DOWFLAKE XTRA calcium chloride per square yard, or 1.23 lbs. of PELADOW calcium chloride. Periodic retreatment, where necessary, is usually accomplished with 1.1 lb. of DOWFLAKE XTRA per square yard.

LIQUIDOW liquid calcium chloride may also be used. Recommended application rate is 0.4 gallons per square yard of 30% solution.

Solid forms of calcium chloride should be spread uniformly, using mechanical spreaders if possible. If the roadway is long, it’s often advantageous to use double-disc lime spreaders attached to a shuttle car. Where the area to be treated is small, a hand-drawn spreader is more practical. If the material is spread by hand, special care should be taken to insure complete blending throughout the haulway surface.

According to time studies conducted by the Caterpillar Tractor Company, about 40% of all time lost by hauling units is caused by poorly maintained haul roads. One particular study revealed this lost time was responsible for a total of $263,000 in lost revenue per year for an operation running six 50-ton trucks. Another $105,000 was reported lost due to equipment breakdowns, many of which were caused by choking dust and rutted, washboard surfaces that put undue strain on vehicles.

Keeps dust down; safety, productivity up

Calcium chloride plays, perhaps, its most important role in mining applications as a maintenance material for haul roads. And it does it all by controlling dust. Here’s how.

As calcium chloride absorbs moisture from the air, it keeps haul roads damp, even on the hot, dry days. It actually becomes a thin liquid coating on each particle of dust, dirt and gravel. As a result, dust particles (called fines) remain in place. You eliminate the problems of slowdowns caused by clouds of dust reducing visibility for drivers. You reduce the chance of equipment failures from dust clogging bearings, seals and other components. And you meet clean air standards for working environments.

Although most states do not have a law regulating “fugitive dust emissions” from surface mines, many of them will in the future. Some states currently set particulate emissions standards and maintain monitors on the mine perimeter to assure compliance. The State’s Environmental Quality Department of the Environmental Protection Agency (EPA) could, in the future, shut a mine down for violating state or federal particulate emission standards, such as the National Ambient Air Quality Standard for Particulates (NAAQS). If not shut down, they could be required to apply “reasonable available control technology” (RACT). Calcium chloride would fit in this RACT niche.

This is all accomplished with far fewer “watering” runs, too. In one case, a company that had been watering all day, every day got better dust control with just one watering application per week after an initial treatment with calcium chloride. Savings were estimated at $228,000 per year.

Cutting maintenance expense through stabilization

Yet, dust control alone tells only half the story. Because, by keeping fines on the haul road, these particles are left to perform the job of binding the surface together. As you know, fines are a very important part of any unpaved road. They add density to stabilize the surface. And that’s where the second chain reaction of benefits begins.

By keeping the road dense, you create a hard, smooth surface that stays that way. Freeze-thaw damage is reduced, so spring road breakup and subsequent maintenance is reduced. Aggregate remains in place so you save on replacement costs. The crown remains intact to assure proper drainage. That, in turn, leads to fewer potholes and less ravel and roll caused by erosion and washouts. It also leads to reduced maintenance costs in the form of fewer bladings. (One firm reduced bladings from once a week to one every three or four months.)

The final result is a haul road that keeps trucks running at maximum speeds for maximum productivity. You eliminate undue wear on tires, shocks and other expensive equipment and parts. You save by reducing watering runs, bladings and aggregate replacement. The total dollar return can be dramatic.

Application rates and methods

Treating haul roads with calcium chloride can be accomplished with existing equipment in almost all cases. General application recommendations are outlined below.

1. Scarify the road to a depth of 3 to 5 inches.
2. Apply LIQUIDOW calcium chloride (30 or 32% solution) to the surface in two or three passes of the water wagon. The total application rate should be between 0.6 – 1.0 gallons per square yard. The amount of DOWFLAKE XTRA equivalent to 0.6 – 1.0 gallons of LIQUIDOW is 2.75 – 5.06 lbs. The preferred application method for treatment with liquid calcium chloride is to windrow the soil after each pass to spread it across the road surface and obtain thorough mixing. A grader is most commonly used to scarify and windrow.
3. Blade the surface to a modified “A” crown to allow water to drain. (In some severe cases, top dressing with approximately 0.1 gallons per square yard of 30 or 32% LIQUIDOW, or equivalent, may be desired.)
4. If available, it is advisable to compact the road surface with a roller, sheepsfoot or other compacting machinery.

Booster applications are recommended every 8-12 weeks or as needed at a rate of 0.2 – 0.3 gallons per square foot.

Another way calcium chloride helps maintain haul roads to minimize lost time is through snow and ice control in winter.

Calcium chlorides urge to return, or remain in its natural liquid state and the fact that it gives off heat as it does so are the properties that make it the most effective deicing material available. Most often, as calcium chloride is used as the highly-concentrated additive to rock salt or abrasives (sand and cinders) to achieve the most economical mix.

Calcium chloride/salt mixtures

When used with salt, calcium chloride serves to make this very inexpensive material work faster and at lower temperatures than it can alone. Whereas salt must be in contact with moisture before it can begin deicing, calcium chloride absorbs moisture from the air so it becomes an effective deicing brine more quickly. Salt is practically effective only down to about 20°F (-6.7°C), while calcium chloride melts at temperatures as low as -30°F (-34.4°C). The result is a deicing combination that’s effective more quickly; that remains effective over a wider temperature range; and that keeps total deicer costs down because less material is needed overall.

Calcium chloride/abrasive mixtures

During very low temperatures, the use of chemical deicers becomes ineffective. Abrasives are then relied upon to keep haul roads open and safe by giving traction aid. The key to fast response with abrasives is keeping them easy to handle. Unfortunately, abrasives tend to freeze and become most difficult to mix, store and handle during the very conditions they are intended to remedy.

Calcium chloride becomes valuable here by preventing moisture in the abrasive mix from freezing. So these materials remain loose, manageable and instantly available. Road crews are able to load quickly and easily from free-flowing stockpiles. Equipment works easily and efficiently without clogging or added strain. You’re able to respond to severe conditions more quickly. No time is lost preparing to treat haul roads so no hauling time is lost.

Calcium chloride also makes abrasives more effective by making them imbed into hard-packed snow and ice instantly. Under many conditions, the treated particles even bore through snow and ice to create a “honeycomb” effect. This makes blading to bare surface possible more quickly. And since each particle imbeds more quickly, there’s less chance for material being lost due to the “whipping” action by wind and traffic. That cuts waste and makes abrasive go farther.

Other Mining Applications for Calcium Chloride

Besides the major applications for calcium chloride outlined in the previous pages, there are a number of other areas where this material’s unique properties are put to use. The following are some examples:

Coal Washing

Calcium chloride is used as a type of “liquid sieve” in the dense media process of coal washing. This process takes advantage of the fact that coal will float in a concentrated calcium chloride solution while rock, slate and other impurities will sink and can be removed.

Other Deicing Applications

Small quantities of calcium chloride are frequently used anywhere men and machinery travel. A few shovelfuls of material can be an aid in creating safe working conditions.

Deicing of coal and ore in storage and in transit

These applications can also return thousands of dollars. The benefits include time saved by keeping material easy to handle and reduced wear on rail cars and conveyors when compared with methods using mechanical force.

Published by the Dow Chemical Company