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<br />Source of CKD Pollutants. Fully "weathered" CKD, whtch is mostly limestone. tends strongly <br />not to release metals when placed to water. If pulverized, metals can be released, but pH should <br />not increase; slight increases in pH would be due to presence of umveathered CKD containing <br />mostly CaO. Release of metals due to pulverization is a surface area effect, alone; any rock. if <br />cn~shed or ground, will release more metal to solution in a fixed period of time than that same <br />rock will release if left uncrushed. Because pulverization generates a high surface area, some <br />"weathered" CKD can release hivh metals. <br />Elements present in clay or limestone prior to [heir kilning for cement manufacture may <br />appear in the dissolved form when "fresh" CKD is placed in water. The major and trace element <br />compositions of the clay and limestone prior to calcining determines what elements may appear <br />dissolved in the water to whtch "fresh" CKD is added. Most of the dissolved metals come from <br />clay, not limestone. As discussed previously, volatile metals [end to concentrate in CKD a[ kilns <br />that employ continuous CKD recycling. <br />Limestone (CaCO}) typically does not contain significant concentrations of trace elements <br />other than strontium because the calcite structure accommodates elements only of specific charge <br />and size. Locally, Zn and/or Ba can be high in some limestones, but most other trace elements <br />appear at low levels. Moreover, limestones selected for cement manufacture typically are chosen <br />for [heir low percentage of impurities (clay and other silicates), so they [end toward more pure <br />limestones -high CaCO~ rocks. Thus, the limestone raw material component cannot contribute <br />much dissolved metal when lime or "fresh" CKD is exposed to water. <br />Clay minerals, however, tend to contain high concentrations of many trace elements, relative <br />to most major rock forming minerals. Informally, clay minerals are termed "collector" minerals <br />because their structures accommodate elements covering the complete range of atomic radii and <br />charge. While these elements may be tightly bound in the clay minerals and not significantly <br />released during weathering, the process of calcining breaks bonds, disrupts the mineral structure, <br />and frees up both the major elements and associated [race elements from the clay minerals. <br />Thus, elements that may be released when CKD is exposed to water come dominantly from the <br />calcined clay minerals. It follows that the pollutants which may derive from CKD in water will <br />differ depending on the type of shale and its particular suite of clay minerals. <br />LEACH TESTING <br />Some of the above characteristics of CKD have become evident in pan through leach testing <br />conducted by [he companies involved. Leach tests conducted on "fresh" CKD differ extremely <br />from "weathered" CKD. The results are characteristic not only of the "type" of CKD but also <br />the leach method. <br />"Weathered" CKD leach tests yielded small amounts of metals by most leach methods, but <br />never high pH. Natural water samples collected below "weathered" CKD piles tended not to <br />show elevated metals or anomalous pH. <br />"Fresh" CKD teach tests produced elevated concentrations of several metals, regardless of <br />the leach test method. "Fresh" CKD also produced high paste pH and leachate solution pH. <br />"Fresh" CKD disposed in ponded water produced a high pH pond. <br />6 <br />