U.S. Borax Inc. Guidelines for Handling and Storage of Borates

1. Handling of Borates in Bulk

Neobor® Borax Pentahydrate: This product is the most stable of the three sodium borates and is ideally suited to bulk transfer. It shows little tendency to cake, except after prolonged storage, or if it becomes severely wetted by rain or other substantial water ingress.

Optibor^® Boric Acids: Optibor Boric Acids are ideally suited to bulk transfer. They show little tendency to cake, except after prolonged storage, or if they become severely wetted by rain or other substantial water ingress.

Borax Decahydrate: Of the sodium borates, Borax Decahydrate is the material that shows the greatest tendency to cake. However, if proper precautions are taken, Borax Decahydrate can be shipped and handled in bulk.

Dehybor® Anhydrous Borax: Dehybor generally handles well in terms of its flow characteristics, but attention must be given to the abrasive nature of the particles. Where large quantities and long-term continuous operation of the unloading plant are involved, preference should be given to mechanical transfer equipment rather than pneumatic systems.

1.1 Bulk Delivery Systems - Railcars, Trucks

Railcars generally have a bottom gate for discharge between the tracks. However, some cars are available equipped for pneumatic discharge either with their own pneumatic systems or utilizing customer's own equipment. The average hopper car is approximately 4,450 ft3 (126 m3 ) and will hold 100 tons (90,700 kg). Cars are available upon request, with dual systems such that unloading can be accomplished using either gravity or pneumatic methods. All cars are equipped with center dump gates.

Trucks are generally equipped with their own pneumatic discharge systems operating at pressures of about 29.4 psi (2 atmospheres) and are capable of delivering into silos up to a height of 100 ft (30 m). Long horizontal runs of piping should be avoided. Containers (either with or without liners) are emptied by gravity or by suction using customer's own equipment.

1.2 Product Unloading

Generally, gravity unloading is more commonly used, especially with those products which tend to cake and form lumps under certain conditions of humidity and temperature such as Borax Decahydrate and to a lesser degree, Neobor.

Gravity unloading is accomplished by discharging product directly from a rail hopper car to a pit located between the rail tracks. It is recommended that an air-operated impact wrench be used for opening and closing the slide gate which can bind with the build-up of product in the slide tracks. Product can then be discharged from the track hopper, at a controlled rate, through an adjustable slide gate to a mechanical conveying system to a storage silo.

Pneumatic unloading is done by vacuum, or combination vacuum-pressure techniques. Neobor and Optibor Boric Acids are non-abrasive and can be easily conveyed by this procedure directly from the car to the silo. A flexible hose with quick coupler is usually attached to a side port on the car with the other end attached to the permanent piping which runs parallel to the silo. This method of unloading has the advantage that the product is not exposed to the elements. Since it is a closed system, contamination from outside sources is eliminated.

Borax Decahydrate contains a higher percentage of water than either Neobor or Optibor Boric Acids and is more prone to caking. While mechanical unloading for Borax Decahydrate is strongly recommended, pneumatic unloading is possible but becomes more difficult. It is strongly recommended that Borax Decahydrate be gravity discharged through a double finger crusher and into a holding bin before being pneumatically conveyed to the silo.

1.3 Transfer of Borates

Mechanical conveying system can consist of belt conveyors, screw conveyors, and centrifugal bucket elevators. Electric or air vibrators mounted near the discharge opening of the track hopper will facilitate discharge if necessary. It is recommended that mechanical systems incorporate sealed transfer chutes and/or dust extraction.

Pneumatic conveying systems have the advantage of being dust-free. Neobor, Optibor Boric Acids and Borax Decahydrate can be air conveyed by pneumatic pipe systems or air slides. Dehybor, because of its abrasive nature, will require the use of ceramic or hard faced liners at specific points where abrasive wear is expected. These include elbows, transition pieces, and impingement surfaces in cyclones, receivers, and diverters. The same precautions noted for the pneumatic unloading of Borax Decahydrate would apply if air slide unloading is to be considered. It is also important that dry and cooled air be used and care be taken to maintain air conveying temperatures below 95°F (35°C). The use of air conveying, for locations that are frequently humid with high ambient air temperatures, is not recommended.

On a small scale, where the unloading equipment is used for short periods only, pneumatic transfer systems can be used, although bends in the pipework should be minimized and where installed, should be constructed of hard-faced or ceramic material. Alternatively, rubberized canvas bends may be suitable.

1.4 Storage of Borates in Bulk

Although most borates can be stored in silos, some borates, such as Dehybor, can cake if storage is prolonged, due to the hygroscopic nature of the material. It should be noted, silo storage of powdered Borax Decahydrate, powdered Neobor and powdered Optibor Boric Acids is not recommended.

Either concrete or mild steel (not recommended for Optibor Boric Acids due to potential corrosion problem) silos may be used. For silos of less than 500 tons capacity, steel construction is possibly the cheaper option. If concrete is preferred it may still be more economical to make the conical section in steel.

2. Handling of Bagged Products

All bagged borate products should be handled with care. Avoid puncturing any bags while using sharp instruments. A hole in a bag not only results in spillage but may allow moist air to enter which can cause caking. The potential for contaminating the products through punctured bags is also greater.

These products are packed in 50 lb. or 25 kg multi-wall kraft paper bags with polyethylene liners. Borates are also available in IBC's (Intermediate Bulk Carriers) in 2,500 lb. or 1,100 kg superbags constructed from white woven 100% polypropylene with or without polyethylene liner.

3. Storage Life of Borates

As long as the products are stored in properly sealed original containers, the storage life (shelf life) is theoretically indefinite since borates will not break down or decompose. If stored under proper conditions, e.g., keeping the container off the floor, away from external heat (temperature < 85°F or 29°C) and humid atmosphere (< 45% relative humidity), a storage life of 3-6 months can be expected. Storage for longer periods are not recommended, although in many cases the products will remain free flowing for up to a year. These guidelines apply to granular products and it is desirable to consider shorter storage periods for powdered products.

For all our products with the exception of Optibor Boric Acids and Boric Oxide (Anhydrous Boric Acid), compatible storage materials are paperboard products, glass, concrete, common plastics and metal materials. Because they are mildly corrosive, contact of Optibor Boric Acids and Boric Oxide (Anhydrous Boric Acid) with mild steel should be avoided. They are, however, compatible with stainless steel and polymer-coated materials.

For additional information, please refer to the U.S. Borax Inc. Technical Service Bulletin entitled "Handling and Storage of Borates."