INSPEC35716

• Permit No: M1977361
• IBM Index Class Name: Inspection
• Doc Date: 12/3/1999
• Doc Name: CEMENT KILN DUST ISSUES OF LONG TERM STORAGE AT LIMESTONE MINES
• From: DMG
• To: BRUCE HUMPHRIES
• Media Type: D
• Archive: No

•
Source of CKD Pollutants. Fully "weathered" CKD, which is mostly limestone, tends strongly
not to release metals when placed in water. If pulverized, metals can be released, but pH should
not increase: slight increases in pH would be due [o presence of unweathered CKD containing
mostly CaO. Release of metals due to pulvenza[ion is a surface area effect, alone; any rock, if
crushed or ground, will release more metal to solution in a fixed period of time than that same
rock will release if left uncrushed. Because pulverization generates a high surface area, some
"weathered" CKD can release hi;h metals.
Elements present in clay or limestone prior to their kilning for cement manufacture may
appear in the dissolved form whin "fresh" CKD is placed in water. The major and trace element
compositions of the clay and limestone prior to calcining determines what elements may appear
dissolved in the water to which "fresh" CKD is added. Most of the dissolved metals come from
clay, not limestone. As discussed previously, volatile metals tend to concentrate in CKD at kilns
that employ continuous CKD recycling.
Limestone (CaCO~) typically does not contain significant concentrations of trace elements
other than strontium because the calcite stnicture accommodates elements only of specific charge
and size. Locally, Zn and/or Ba can be high in some limestones, but most other [race elements
appear at low levels. Moreover, limestones selected for cement manufacture typically are chosen
for their low percentage of impurities (clay and other silicates), so they tend toward more pure
limestones -high CaCO~ rocks. Thus, the limestone raw material component cannot contribute
much dissolved metal when lime or "fresh" CKD is exposed to water.
Clay minerals, however, tend to contain high concentrations of many trace elements, relative
to most major rock forming minerals. Informally, clay minerals are termed "collector" minerals
because their structures accommodate elements covering the complete range of atomic radii and
charge. While these elements may be tightly bound in the clay minerals and not significantly
released during weathering, the process of calcining breaks bonds, disrupts [he mineral structure.
and frees up both the major elements and associated trace elements from the clay minerals.
Thus, elements that may be released when CICD is exposed [o water come dominantly from the
calcined clay rinerals. It follows that the pollutants which may derive from CKD in water will
differ depending on the type of shale and its particular suite of clay minerals.
LEACH TESTING
Some of the above characteristics of CICD have become evident in part through leach testing
conducted by the companies involved. Leach tests conducted on "fresh" CKD differ extremely
from "weathered" CKD. The results are characteristic not only of the "type" of CKD but also
the leach method.
"Weathered" CKD leach tests yielded small amounts of metals by most leach methods, but
never high pH. Natural water samples collected below "weathered" CKD piles tended not to
show elevated metals or anomalous pH.
"Fresh" CKD leach tests produced elevated concentrations of several metals, regardless of
the leach test method. "Fresh" CI{D also produced high paste pH and leachate solution pH.
"Fresh" CKD disposed in ponded water produced a high pH pond.
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