Foraging for foundry sands

Published: Tuesday, 22 November 2011

Metalcasting consumes vast quantities of industrial minerals – either as foundry sands or additives – which are subsequently landfilled. But simple processing of spent sands can provide a stable and valuable source of secondary foundry materials

Recycling - it’s a sign of the times. From paper and plastic products to electronic wastes and metals, the recycling movement is growing. There is one company that has now brought this concept to the industrial minerals field. Alexander Mill Services International Inc. (AMSI), based in Harmony, Pennsylvania, USA has been supplying the foundry, refractory and special minerals industries with reclaimed products since 2005.

AMSI’s involvement with chromite reclamation began in July 2003, when Tom Vlajkovich, a broker for American Waste Management Services, contacted the company about its interest in the reclamation of a hazardous waste landfill in Ohio.

“He posed the question; can you reclaim chromite sand from silica sand,” John Alexander III, president of AMSI, told IM. “Yes I said, yes I can. I did not want to miss the opportunity, and although I was not even vaguely aware of what chromite sand was at the time, I was certain that given our past experience, it would be easy. Little did I know how wrong I was about to be.”

From 1967 until 1994, the Ohio landfill site was utilised as a dumping facility for a large steel foundry’s waste sand, steel scrap, slag and iron oxides, as well as sludge from its sand washing process. The sludge was generated as a slurry from washing sand that used a bentonite clay binder in the foundry’s ‘green sand’ system. Bentonite clay has the capability to hold several times its dry mass in moisture, a property which makes it one of the most difficult materials to process.

Core room chromite

Original estimates placed the landfill volume at over 600,000 tonnes with chromite estimated at 30% and the bentonite clay sludge at 20%. Also included in the landfill was electric arc furnace (EAF) dust. The EAF dust, due to its potentially high concentrations of barium, cadmium and lead, caused the landfill to be listed as a hazardous waste site. Working in conjunction with the Ohio Environmental Protection Agency or OEPA, the focus of the project was to process the material in the landfill with the intention of reclaiming the valuable chromite sand for reuse at the foundry, while testing the process outflow to guarantee that no harmful constituents were present. The project was scheduled for completion over a seven-year period.

In preparation, AMSI was provided with chemical analytical and sieve sizing information outlining the desired limits acceptable in the reclaimed chromite product. Utilising this information as a starting point, AMSI contacted equipment specialists to explore the possibility of creating a system capable of handling the material. Mc Lanahan Corp., based in Hollidaysburg, PA, was chosen for its expertise in wet density separation and Eriez Magnetics, in Erie, PA for its specialised magnet experience.

In gaining a better understanding of the foundry material, a more clear vision of how to take advantage of its inherent properties was gathered. The most important aspect of this observation was that all of the sand products arrived at the foundry as a specification product. It was AMSI’s job to remove the residual impurities, including the binders, slags and oxides, from this material and bring it back to as close to specification as possible.

Process development

AMSI initially focused on the obvious density and magnetic separation differences between the chromite, silica and other highly and mildly magnetic materials. Laboratory tests showed very promising results, and the decision was made to move forward with the project. The facility became operational in August 2005.

“To say that we were plagued with problems from the onset would be an understatement. It was immediately realised that the information that was provided to us regarding the landfill values was inaccurate. New core borings taken at the facility after we had begun operations showed that the sludge content was higher than 50% as opposed to the 20% that was documented,” Alexander explained.

The chromite content was also dramatically different at roughly 6% compared to the listed 30%, while the bentonite caused serious problems from a processing perspective. Due to the ultrafine nature of the material, a specialised blend of sulphuric acid, coagulants and polymers had to be developed in order to solidify the material.

AMSI worked with a number of chemical companies in the USA in an effort to solve this problem. The site currently uses a proprietary flocculent, supplied by Chemtreat, which was developed specifically for this application.

The bentonite overwhelmed the dewatering equipment which had been designed for lower output. Without the appropriate equipment, it appeared that the project would fail prior to even becoming fully operational. It was only with the cooperation of the OEPA that AMSI was allowed to create large holding ponds to store the sludge on site, solving this problem.

“The problems that we had encountered with the material up to this point had severely hampered our ability to create the product quality that we had originally intended and we had to approach our customer with the concept of utilising a lower grade chrome product,” Alexander said.

As the foundry that had generated the material had intended to utilise the chromite as blend sand in its green sand system, the product quality was acceptable for this process and the foundry became the first, and for a while, only customer of AMSI’s reclaimed sand product. The company was joined shortly thereafter by a sister company that had similar sand needs.

As production increased, AMSI needed to expand its sales horizons. Initial attempts to market the product further into the foundry industry had failed, due not only to the higher than specification silica content, but more importantly, to the high acid demand value (ADV). As the original chemical analysis report that was provided did not include an ADV test, AMSI did not make this a part of its testing protocol and therefore did not have the necessary separation technologies in place to tackle this issue. This oversight had created a significant problem in attempting to manufacture a chromite product that could be used interchangeably with new material.

In 2007, AMSI started to evaluate secondary technologies that could remove the mildly magnetic/ high calcium slag materials that were creating the ADV issues. It was determined that although the slag and chrome had equivalent magnetic attraction properties, they had different specific gravities. To this end, AMSI had determined that air separation technologies would not only solve this problem, but would best fit the profile of its facility.

Alexander and the company’s plant manager, Mark Sowers, discussed Oliver Manufacturing Co. separation equipment in great detail. At the time, most people equated Oliver machines with agricultural separation.

“More than a few people thought that we were a little crazy for wanting to use Oliver machines to purify chromite. Regardless, Mark and I made the trip to Colorado and spent two days working with Jim Thomas, design engineer for Oliver, in proving that this concept could work,” revealed Alexander.

The company installed Oliver air bed separators in 2008. With these units in place, AMSI was capable of producing chromite sand that met much more stringent specifications.

Upon review of available chromite specifications, AMSI chose to follow the Steel Founders’ Society of America, Tentative Specification for Chromite Sand and Flour (SFSA 16-T67) issued in 1967 (Table 1).

AMSI is producing a product that easily meets these specifications. The company has continued to strive to improve product quality, and has made recent improvements in its processing technology. These changes were made in answer to a problem discovered during extensive research, wherein the chromite sand that has been in contact with the highest heat from the steelmaking process goes through a slight conversion phase and exhibits characteristics that are out of specification with new chromite.

AMSI’s processing changes have given it the ability to separate this ‘spent’ material, with successful results - an overall lowering of the silica content and an increase in the chrome units.

It is often asked if AMSI chromite is a realistic alternative to new chromite: AMSI currently has 14 customers in the US foundries and refractory markets, with more companies in various phases of testing its product, that have made the chromite a critical part of their supply chains.

Reclamation overview

The company’s goal is to continue to create reclaimed chrome products that meet the needs of the foundry, refractory and chemical industries. In order to accomplish this goal, AMSI is researching other avenues to gather waste chrome products. It monitors and documents foundry landfills opportunities - as this is the core of the company’s new business model - and is also in discussions with operating foundries on the installation of in-house separation systems that can strip the chrome and oxides from the silica sand.

AMSI has also worked with core manufacturing facilities and foundries to collect scrap cores for reuse, and continues to evaluate reuse potential for refractory wastes and other chrome bearing materials.

“We see every pound of chromite that comes into these facilities as a resource that can be used many times over, stretching the life cycle of this material almost indefinitely,” Alexander commented.

In each of the scenarios in which reclamation is an alternative, it is critical to evaluate all possible revenue sources that are a part of the total. Foundry landfills can contain ferrous and non-ferrous scrap, iron oxide, steel shot, carbon electrodes, zircon and chromite sands. With the increasing interest in reclaimed proppant (fracturing) sands used in the oil and natural gas industry, it important to note that the largest constituent of the landfill itself, the silica sand, could possibly be one of the highest revenue generators.

Although each landfill would require specialised separation technologies designed to capitalise on its own inherent properties, many of these pieces of processing equipment can be utilised in different combinations as needed on different projects. This compartmentalised approach is fundamental to keeping installation, as well as investment, costs in line.

AMSI has done extensive research on many foundry properties and found that in a typical foundry landfill operation, processing 10,000 tpm could yield the following results as shown in Table 3.

This plant capacity is in keeping with AMSI’s Ohio facility which operates at 50 tph. It is not hard to visualise how a larger plant, such as a 200 tph operation, could significantly shift the dynamics of this model. Processing 40,000 tpm could yield the following results as shown in Table 4.

As Table 4 shows, expanding on this concept changes the dynamics quickly. Although it would cost roughly twice as much to build a 200 tph plant versus a 50 tph plant, revenue would quadruple, while operating costs, as a percentage of revenue, would be reduced by more than half.

In many of these landfill scenarios, the foundry is under a state or federal order to remove some or all of the sand from its facility. In these cases it may be possible to negotiate a processing fee that would cover many up-front costs, once again, lowering overall costs and boosting potential profit.

Because chromite is not AMSI’s only product, the pricing of the material is less contingent upon outside factors such as availability or transportation costs, but more in line with current chromite pricing. In recognition of the fact that the company offers a reclaimed product, AMSI continues to sell this material for lower than market value.

Foundry landfill site in Ohio, USA

Hub and spoke concept

In an effort to more efficiently and cost effectively reclaim materials, AMSI is in the process of building smaller scale, highly efficient ‘scalping’ plants that can separate the valuable chromite, as well as other reclaimable products, from the sand. Once these materials are removed, they can be transported to a hub facility, similar to the operation in Ohio, where they can undergo secondary processing, packaging and shipping. In this manner, numerous small jobs can be operating in a set geographic area while keeping large investment overhead and transportation costs to a minimum.

AMSI continues to push the boundaries of reclamation technologies. The company is the first of its kind to sell a recycled chromite product, the first to sell a recycled iron oxide substitute and the first company to have a recycled silica product approved by the American Petroleum Institute. In the course of this work AMSI continues to diminish unsightly and potentially dangerous landfills while saving companies money on much-needed materials.

John Alexander III, president, Alexander Mill Services International Inc., Pennsylvania, USA.

Spotlight on Alexander Mill Services International

Founded in 1981 by John S. Alexander Jr., AMSI provides recycling services to steel mills and foundries. These services include the removal of slag from the steelmaking process, as well as the reclamation of ferrous and non-ferrous metals from the waste slags and sands that have been generated by these facilities. The steel products are recycled back into the facilities’ melting process, while the slag and sand products are used in alternative aggregate applications.

AMSI has performed these services throughout the USA at 17 operations, including Nucor Steel, Structural Metals, and Florida Steel and throughout Europe at 13 operations, including Huta Ostrowiec in Poland, COST in Romania, Halyvourgia Thessalias in Greece and Siderugia Nacional Empresa in Portugal.