= Incongruent dissolution
<Incongruent dissolution> occurs when a solid releases its constituents into solution in proportions different from its bulk <stoichiometry>. Preferential release of one constituent, or dissolution accompanied by formation of a secondary solid, can both produce this behaviour.
For a nominal solid $A_aB_b$, congruent release would give dissolved amounts in the ratio $a:b$ if no other sinks intervene. An outlet ratio different from $a:b$ therefore motivates checking for selective leaching, precipitation, adsorption and surface alteration. It does not alone prove which step controls the rate. Distinguishing these processes matters when using a <single-pass flow-through leach test> to infer long-term durability from measured solution concentrations.
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