68    CONTROL OF CARBIDE LEVELS IN DESULFURIZATION
OF GREY IRON SO SLAG WILL BE NON-HAZARDOUS
James E. Etzel, Professor
School of Civil Engineering
Purdue University
West Lafayette, Indiana 47907
William Kodatsky, Product Manager
Cyanamid Canada, Inc.
Markham, Ontario
Canada L3P 3J5
Joseph B. Medved, Administrator
Environmental Activities
General Motors Corporation
Saginaw, Michigan 48605
INTRODUCTION
In order to produce the quality of product required for nodular iron castings, the normal sulfur
level of grey iron must be reduced. To achieve the reduction, it is desirable to use calcium carbide to
destroy or liberate the sulfur from the molten iron. The initial efforts which were to be accomplished
were to treat the carbide containing slag with an excess of a sulfur compound. This treatment was
intended to drive the reaction with the carbide to completion. The treatment should have left no
residual carbide to produce acetylene on contact with moisture from the air or from water quenching
of the slag. By driving the reaction to the point of zero residual carbide, where acetylene generation
would not be possible, the slag would not be a hazardous waste. The actual form of the sulfur in the
metal was unsure. This made it unclear whether the carbide destruction of sulfur was an oxidative or a
reductive process. In view of this fact, two forms of excess sulfur to drive the reaction to the point of
zero carbide residual were considered for use. One was calcium sulfate and the other sodium hydro-
sulfide.
Prior to testing of the proposed procedures for sulfur addition, the program was modified by the
introduction of a new modified calcium carbide. The material, produced by Cyanamid Canada, Inc.,
was a new compounded form of carbide with properties which allowed it to approach total consumption during the desulfurization process, thus minimizing any excesses in the resulting slag. In view of
the promise of this material, the testing was redirected to evaluations of modified calcium carbide
residuals obtainable in actual full scale desulfurization trials.
A test procedure for acetylene generation potential of a slag had been developed by Cyanamid
Canada. When subjected to a close evaluation, this procedure proved to be less sensitive than
required. A new testing procedure, using a portable gas chromatograph and a trapped volume of air,
was evolved. This procedure was to be sensitive enough to measure the levels of acetylene at 1.0% or
less of the lower explosive limit (LEL). The details of the procedure will be presented later in this
chapter.
The final part of the effort was to run acetylene measurements on slag samples from test runs of the
desulfurization procedure using the modified carbide. Data from these tests were developed and
compared with the desired levels of acetylene as established by a consensus of General Motors
Corporation staff and other parties associated with the evaluation program. An agreed acetylene level
was necessitated by the absence of any specifics on acetylene in the RCRA regulations. Other than the
flammable-explosive classification which applied, no specifics on acetylene were found to be available. In order to arrive at an agreed acetylene level, many factors regarding the desulfurization
process and its operation had to be considered.
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.