= Single-pass flow-through leach test
= SPFT leach test
{synonym}
A <single-pass flow-through leach test> measures the <dissolution> of a solid while fresh solution continuously enters a reaction cell and the outlet solution is collected for analysis. Unlike a closed vessel, the cell continually exports dissolved constituents. A reported implementation uses a pump, a solution reservoir, a reaction cell and controlled <temperature>.<Low-Activity Waste Glass Studies: FY2000 Summary Report by B. P. McGrail and others>[PNNL-13381, section 2.1.3, Single-Pass Flow-Through Test]{ref}
At <steady state>, an elemental <mass balance> gives the normalized release rate
$$
r_e=\frac{Q(c_{e,\mathrm{out}}-c_{e,\mathrm{in}})}{f_e S},
$$
where $Q$ is the volumetric <volumetric flow rate>, $c_e$ is the <mass concentration> of element $e$, $f_e$ is its initial <mass> fraction in the solid, and $S$ is the exposed <surface area>. For example, using litres per day, grams per litre and square metres gives grams of equivalent solid per square metre per day. This expression follows by dividing the exported elemental <mass> per day by $f_eS$.
Changing $Q/S$ changes the accumulation of dissolved material and therefore the <chemical affinity> for <dissolution>. A rate independent of further increases in $Q/S$ can help identify a dilute-solution regime. Different elemental release rates can also reveal <incongruent dissolution> or retention in <secondary phases>, so interpreting a release rate as whole-solid loss requires an explicit material model.
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