Sand reuse & reclamation: disposal alternatives for today.

Sand Reuse & Reclamation: Disposal Alternatives for Today

Over 130 foundrymen met recently to hear how the Ontario Ministry of the Environment is assessing foundry sands for potential reuse and to hear about the latest trends in sand reclamation. "The International Conference on the Reclamation and Reuse of Foundry Sands," cosponsored by the Steel Castings Institute of Canada (an affiliate of the Canadian Foundry Association) and the American Foundrymen's Society, took place April 6-7 in Toronto.

Reuse Studies

The Ontario Ministry of the Environment is proceeding in its development of a protocol for waste sands, reported Robert J. Dalrymple, Ontario MOE, Toronto. MOE is readying its "Guidelines for the Utilization of Industrial Wastes in Backfill and Construction Applications," which includes use guidelines for foundry sands.

Dalrymple said that foundry sands which meet already established MOE leachate guidelines may be suitable as backfill for agricultural and parkland, residential and commercial/industrial uses, depending on the chemical compositions. For example, agricultural and residential uses will require sands that have much lower residual elemental compositions than those used in industrial sites.

During Phase One of the project, a tentative waste classification process was developed based on results of bulk quality and leachate characterization tests. Based on these results, a "Schedule of Acceptable Wastes and Uses" has been recommended.

Phase Two of the project was developed to establish the effectiveness and reliability of the proposed guidelines through field studies at selected sites. The foundry sand field study was described at the conference by Maria Kelleher, Canviro Consultants, Mississauga, Ontario, which is conducting the study for MOE.

The foundry site chosen for this study is located outside Hamilton, Ontario, adjacent to a gray iron foundry, Kelleher said. The foundry is disposing of shell core and green sand in a marshy area that is being reclaimed.

Studies of the site, which began in the Fall of 1988, consist of hydrogeologic investigations, groundwater sampling and analysis and backfill material sampling and analysis. According to Kelleher, "The results of the field program will be used to judge the effectiveness of the tentative guidelines, which will then be modified, as appropriate, based on the field program results."

Waste Disposal

Because landfill tipping fees are rising in Ontario, as they have across the U.S., many Ontario foundries are taking a serious look at alternate use, waste minimization and sand reclamation, said Michael Promoli, Crowe Foundry, Ltd, Cambridge, Ontario. Promoli said the Sand Reuse and Reclamation Committee of the Canadian Foundry Association is becoming more active in analyzing these options.

"Landfill is the least preferred method of waste disposal," Promoli commented. "Waste reduction must come first. Sand reclamation is the cleanest and best route to foundry waste reduction," he concluded.

Kelsey-Hayes Canada, Ltd, is one foundry that has solved its near-term disposal problems by developing its own licensed landfill site. Tony Pignon, Kelsey-Hayes Canada, described the foundry's numerous explorations of waste minimization alternatives, brought about by surcharges for excessive quantities at the landfill they had been using.

As the sand is nonhazardous, the foundry attempted to reuse their waste in different product forms, i.e., backfill, highway fill, fertilizer and cement blocks from slag, but none proved feasible at the time.

As the company desired time to study the various reclamation options further, it chose to develop its own landfill site. A very suitable site was located in a disused gravel pit and the landfill was developed to MOE guidelines. The new facility has a 400,000 ton capacity, giving Kelsey-Hayes 17 years of cost-effective waste disposal capacity, Pignon reported.

Sand Reclamation

In the U.S., several factors are combining to make reclamation more attractive than reuse or landfill disposal. In the view of Robert Zayko, RMT, Inc, reuse applications may be too few in the future to provide a viable disposal alternative. "Reuse is only an interim measure," he said. "The time of reclamation is drawing closer for more and more foundries."

Growing scarcity of disposal sites, rising transport costs and disposal costs all are trends on the increase. For example, nonhazardous landfill fees in Michigan have risen from $20/ton in 1981 to $120/ton in 1987. Today, Zayko said, fees are closer to $150/ton. As for hazardous waste disposal, all land disposal of untreated hazardous waste will be banned by May 1990. This development alone is pushing foundries toward reclamation, he said.

What is involved in sand reclamation? Daryl Hoyt, Wedron Silica Co, answered by stating that, "A foundryman needs to realize that there's a lot more to sand reclamation than just purchasing the reclaimer.

"For example, you probably already have a shakeout unit, but the shakeout units in most foundries don't adequately break the refuse sand down to the size needed to submit for pneumatic, mechanical or thermal type reclamation systems," Hoyt explained.

"Most foundries will need to add a crushing step to break down and particulate the shakeout sand into individual grains of sand suitable for scrubbing and classifying," Hoyt added. Figure 1 shows the flow of sand through the processing equipment needed for a mechanical or pneumatic reclamation system.

Several reclamation equipment suppliers, most of whom were presenting thermal reclamation units, provided equipment descriptions.

Most speakers noted that the current trend in new sand reclamation systems today is a combination of mechanical or pneumatic and thermal reclamation. Many foundries today run several types of binder systems in mold and core operations, but combine all waste sands in the shakeout. For economy, the sands must be reclaimed together.

If all the sand is organically bonded, a thermal system may suffice. But clay bonded sands and inorganic binders, such as sodium silicate, need mechanical or pneumatic scrubbing to remove the thermally degraded inorganic coatings. Combination systems give the foundry the flexibility it needs in reclaiming a wide range of bonded sands.

Binder Development

Developments in chemical binder technology have improved the reclaimability of two popular binder systems. Derrick Bayles, Foseco, Ltd, described developments in these low polluting, inorganic sodium silicate processes.

Liquid co-binders, which provide faster strip time at higher strengths and which also improve shakeout and reclaimability, have been introduced. For air-set silicate systems, a liquid ester hardener is added to the sand prior to the introduction of the sodium silicate binder.

A new reclamation process for the ester silicate sand has shown improved performance over reclamation of earlier acetate ester silicate systems, which tended to fracture sand grains. Instead, an alkylene carbonate ester is used with a modified sodium silicate binder. This new process forms a pseudo-crystalline binder film on the sand grains, which become brittle at high temperatures.

This reaction results in formation of microcracks in the binder during sand drying. Mechanical attrition reclamation permits binder removal without significant grain fraction. Thus, sand drying, prior to attrition, is a necessary step in a reclamation system for this type of binder.

An investigation into the low rebonding strengths of reclaimed phenolic ester bonded sands was described by S. Raja Iyer, Acme Resin Corp. The work established that the low rebonding strengths of these sands were due to the presence of a thin film of chemical compounds that covered the sand grains, forming a barrier to the adhesion of resin to the grains. The barrier is not totally removed by mechanical and thermal reclamation techniques.

He then described a chemical treatment technique that significantly reduces the effect of the barrier on mechanically and thermally reclaimed sands. The new liquid chemical product is used as a third component, or pre-bond additive, in conventional mixing of reclaimed phenolic ester sands. Rebond strengths and mold hardnesses with these reclaimed sands showed significant increases when the new liquid additive was used.

Other speakers on the program included John Perrins, Ashland Chemicals Resins and Chemicals Division and Ezra Kotzin, American Foundrymen's Society. Reclamation equipment presentations were provided by John Garrick, C-E Cast Equipment; Marvin Evans, College Research Corp; David Silsby, GMD Engineered Systems; Bill Gudgeon, Gudgeon Brothers, Ltd; Russell Kelly, Industrial Filter Fabrics, Ltd; Dennis Minnich, Pangborn/Sohio Co; David McDonald, Quiptec, Inc; Stewart Jackson, Renew Foundry Equipment, Ltd; William Zatkoff, Sand Technik; Denis O'Shaughnessy, Simplicity Engineering Co; and Dieter Leidel, Tanoak Enterprises, Inc.

PHOTO : Fig. 1. Processing equipment needed for a mechanical/pneumatic reclamation system is shown.

PHOTO : Proposed land use standards for foundry sands are being developed by the Ontario Ministry of the Environment, explained Robert Dalrymple, Ontario MOE.

PHOTO : "Make sure the reclamation system you choose is effective in removing the residual binder," advised Daryl Hoyt, Wedron Silica Co.

PHOTO : Ron Shaw, DOFASCO, Inc, Hamilton, Ontario, stressed the importance of finding ways to reuse and reclaim foundry sands. "Use of landfill sites is becoming limited and expensive," he stated.