Elemental phosphorus recovery:\nApproximate overall yield of elemental phosphorus obtained from rock phosphate by thermal reduction in an electric furnace is typically in which range?

Introduction / Context:
Elemental phosphorus (usually white or yellow P4) is produced industrially by carbothermal reduction of phosphate rock with silica and coke in an electric furnace. Understanding typical material yields helps in evaluating process economics, energy use, and byproduct handling (silicate slags, fluorine compounds). This question asks for the approximate overall yield range realized in practice from rock phosphate feed.

Given Data / Assumptions:

• Feed: beneficiated phosphate rock with typical P2O5 content.
• Process: high-temperature electric furnace reduction with coke and silica.
• Yield refers to elemental phosphorus recovery relative to phosphorus content of feed.

Concept / Approach:
In the thermal route, not all phosphorus in the rock is recovered as P4 due to incomplete reduction, volatilization losses, and retention in slag phases. Operational data commonly place overall recoveries in the mid ranges rather than near 100%. Among the presented options, a 60–65% yield window is representative of practical, large-scale furnace operation when considering feed variability and process constraints.

Step-by-Step Solution:

Verification / Alternative check:
Industry summaries and textbook examples cite recoveries well below 100% for the electric furnace process, with improvements possible through feed preparation and furnace control but typically not approaching the 90–95% figure in routine operation.

Why Other Options Are Wrong:

• 1–2% and 15–25%: far too low for an established industrial process.
• 40–45%: underrepresents feasible recoveries.
• 90–95%: overly optimistic given real plant losses.

Common Pitfalls:
Confusing elemental phosphorus yield with fertilizer-grade phosphoric acid yields from “wet process,” which follow different chemistry and recovery metrics.

Final Answer:
60–65%.