Why is zone refining usually impractical for purifying tons of metal each day?

Zone refining is generally impractical for the large-scale purification of metals—such as processing tons per day—primarily due to the process's inherent speed and thermal limitations.

The technique is a relatively slow physical separation method, with typical freezing rates for inorganic substances ranging from only 0.5 to 30 centimeters per hour. Furthermore, because metals possess high thermal conductivity, the process suffers from excessive heat loss, making it inefficient for high-volume industrial metal production. While it is highly effective for achieving ultra-high purity in materials like semiconductors, its use is typically reserved for preparing high-purity materials in limited quantities rather than bulk industrial processing.1

In contrast, zone refining is considered feasible for organic compounds on a tonnage scale, largely because those materials exhibit very low thermal conductivity.1