Passing solubility criteria

These metals are considered hazardous under the Resource Recovery and Conservation Act of 1987 (RCRA) [4]. The RCRA metals occur in chemical forms that are soluble or insoluble in groundwater. The soluble species are of concern from the dispersibility viewpoint. Hence, the test criterion to evaluate whether a given waste stream needs stabilization prior to disposal is based on how much a given hazardous metal dissolves in water in a standardized test. This EPA test, called the Toxicity Characteristic Leaching Procedure (TCLP) [5], is used not only to identify which waste streams need treatment, but also to assess whether the treated waste form is suitable for disposal. This test also sets limits on how little of a hazardous metal is permitted to leach out from a given waste to pass the waste for disposal. If the test determines that the waste is not suitable for safe... 

An additional selection criterion is a detectable metastable zone width. Every solution has a maximum amount that it can be supersaturated before becoming unstable. The zone between the solubility curve and the unstable boundary is referred to as the metastable zone. In an initial seeded batch the supersaturation is always maintained within the metastable zone to minimise nucleation, the formation of new unwanted tiny crystals known as fines. These either cause filtration problems or reduce batch yields by blocking or passing through screens. 

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