Using Aluminum Oxide in Recycling

Washington Mills has developed a process that allows it to collect spent aluminum oxide and recycle it back into the manufacturing process.

Every year, over 150,000 tons of fused aluminum oxide is consumed in the U.S. Only a very small portion of that is recycled. Prices for the raw materials used to manufacture fused aluminum oxide have increased to the highest levels in history. Bauxite, for example, has become increasingly harder to source and, in the past year alone, prices have more than doubled.

China is a major supplier of bauxite and has experienced a mix of pivotal events which have contributed directly to upward pressure on bauxite prices. These pressures include increased Chinese domestic demand for bauxite in the aluminum industry, rapidly rising Chinese power costs, plant closures, increased transportation costs, and stricter environmental controls on calcined bauxite. The economic case for the recycling of aluminum oxide has been strengthened by this paradigm shift.

Spent aluminum oxide is traditionally brought to the landfill for final disposal. However, tighter landfill regulations, higher freight costs and rising landfill costs are causing businesses to rethink their waste disposal practices.

Washington Mills is one of the largest manufacturers of aluminum oxide in the U.S and, as such, is aware of the growing need to find a better way to dispose of spent abrasive grain. In an attempt to address this problem, Washington Mills has worked with large-volume users of its BLASTITE® BT abrasive blasting grain to collect the spent aluminum oxide and recycle it back into the manufacturing process.

Closed-Loop System

Significant research and development resources have been invested by Washington Mills to make the manufacturing of aluminum oxide a completely closed-loop system. Although other industry players chose to close down their aluminum oxide furnaces and source or produce from China, Washington Mills strategically decided to continue the manufacture of fused aluminum oxide in North America. Now, it is the only manufacturer of fused aluminum oxide in North America and operates its furnace plants, meaning the spent aluminum oxide can be reintroduced into its furnace operation.

Blasting grain produced by crushing chunks of fused alumina.

Blasting grain produced by crushing chunks of fused alumina.

The spent aluminum oxide grit in the Washington Mills’ recycling program is reused as an ingredient for making new fused aluminum oxide. The spent aluminum oxide is mixed with new bauxite, and the mixture is fed into furnaces that have been specially designed to melt and purify the liquid abrasive. The company has furnace expertise that enables it to transform the spent aluminum oxide back into the raw materials that are needed to make pure fused aluminum oxide. This is a 100% closed-loop manufacturing system because the aluminum oxide is recycled back into the furnace that it came from originally and used to make new fused aluminum oxide.

Recycling Challenges

Over the years, Washington Mills has worked to modify its furnace operations to accommodate the spent aluminum oxide. It is not a simple process to furnace aluminum oxide because it requires the furnace to be charged with a raw material mix that has the correct stability and chemistry for the materials to fuse safely and effectively. When non-virgin organic materials are introduced, for example spent aluminum oxide, the chemistry of the raw material mix changes constantly. It is important to be diligent about testing the recycled materials and mixing the right ratio of materials to achieve the desired chemistry because the furnace process cannot reduce certain chemistries.

An electrode supplies power (center) while raw materials are added to a furnace via feed chute (right).

An electrode supplies power (center) while raw materials are added to a furnace via feed chute (right).

A furnace operator takes a sample before pouring the liquid aluminum oxide.

A furnace operator takes a sample before pouring the liquid aluminum oxide.

Before the grit can be accepted for recycling at Washington Mills, it has to undergo a strict testing program. The chemistry of the material is tested by the company until it is certain that the material will work in the furnace process. The spent abrasive grain may contain different metals or other elements that it picked up in the blasting process. This is dependent on the surface being blasted. The small amount of debris in the spent grain does not cause a problem in a lot of applications. However, where cadmium, lead, or other elements were taken off in the blasting process, the material would not be used for recycling.

With each new shipment, the recipe changes and so a sophisticated technical process was developed to allow the company to handle the variety of particle sizes and chemical compositions of the spent material. Washington Mills continually improves the management of the materials and adapts the mix of raw materials to suit the furnace process. The company believes innovation by adapting the process to work with alternative sources of materials provides a manufacturing edge.

Often, the spent material is returned in much finer particle sizes than raw material. It is challenging to achieve handling capabilities that can manage materials of very fine particles sizes and also myriad packaging types. Finer materials are harder to handle and often need to be agglomerated before they are fed into the furnace. A considerable amount of work must be done to prepare very fine material before use because it does not move well or release easily into the furnace. Additionally, the material is returned in a variety of different package types, from sacks to drums to bulk, and this makes operating an efficient material handling system challenging.

Widespread Benefits

Although it is challenging, recycling programs are beneficial in terms of offering a greater level of service to customers and in manufacturing a high-quality, competitively priced product in North America. In the current climate of soaring electricity and raw material costs, and the declining quality of raw material inputs, a recycling program that minimizes dependency on expensive raw materials to control cost offers real value to users of fused aluminum oxide.

By refining its closed-loop system, Washington Mills believes that it is helping customers escape the one-way landfill trap of rising disposal costs. The company aims to maximize the customer experience while innovating itself away from rising manufacturing costs by bringing the spent material back into the furnace and transforming it into fused aluminum.

Case in Point

For a blasting application, one heavy manufacturing company was using approximately 500 tons of fused aluminum oxide grit annually. The landfill costs were $60 per ton (cost differ with geographical location) and so the company was spending $30,000 per year to put the spent aluminum oxide in the ground. Washington Mills was contacted to see if it could recycle the material. Washington Mills tested the spent grit and it was determined as being suitable for recycling.

The company developed a simple collection system to gather the spent grit and started sending the material back to Washington Mills so that it could be reused in the recycling program. Both parties reduced their impact on the environment, and the company was able to eliminate its landfill costs. Furthermore, Washington Mills made a step towards reducing the cost of its raw materials. In the face of rising prices for raw materials, this is a step towards controlling costs for the benefit of both the customer and the manufacturer.

Ready, Set, Blast

The metal preparation and finishing industry is a primary consumer of fused aluminum oxide. In this application, it is used as an abrasive blasting media. When propelled by air pressure, the grains of fused aluminum oxide become a powerful, multi-edged, abrasive tool, that penetrates workpieces, leaving clean, etched surfaces in their wake. Contaminants and unwanted substances are removed from the surface of the metal by the abrasive particles, giving it the desired finish. Blasting with fused aluminum oxide is a very effective method either for material removal or surface preparation on many different surfaces, including alloys, metals, ceramics, glass, granite, marble, and other stone.

BLASTITE BT blasting grain from Washington Mills is an abrasive grain used in the blasting industry. In pressure blasting, a pressurized stream of compressed air is directed onto a workpiece through a nozzle to create a uniform surface. The blasting is either done in a large blast room or a blast cabinet that contains and collects the aluminum oxide after it has been blasted onto the part.

Depending on the desired surface profile or the piece being blasted, the aluminum oxide may be collected and reused for multiple passes through the blasting system to maximize the abrasive life of the grain. When the abrasive particles have been reduced in size, the aluminum oxide is either sent to Washington Mills for recycling or disposed of in a landfill.

This information has been sourced, reviewed and adapted from materials provided by Washington Mills.

For more information on this source, please visit Washington Mills.

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