Mineral processing: The operation used to remove clay and other impurities adhering to iron ore prior to further processing is called

Introduction / Context:
Before iron ore is subjected to high-temperature processes, it is first cleaned and sized. This initial step, known broadly as ore dressing or mineral processing, improves feed quality to downstream kilns and furnaces and reduces fuel consumption and emissions.

Given Data / Assumptions:

• The question focuses on removing surface impurities like clay and adherent soil.
• No chemical transformation is intended at this stage.
• Subsequent thermal steps (calcination, roasting, smelting) are separate operations.

Concept / Approach:
Identify which named operation addresses physical cleaning. Dressing encompasses washing, screening, jigging, and other physical methods to separate impurities from the ore without chemical reactions. Calcination and roasting alter ore chemistry or mineral phases, while smelting produces molten metal.

Step-by-Step Solution:
Define the goal: remove clay and loose impurities.Match process type: physical separation and washing → dressing.Exclude thermal processes: calcination (drives off CO2 from carbonates), roasting (oxidation/sulfide conversion), smelting (reduction to metal) are not simple impurity removal steps for clays.Therefore, the correct operation is dressing.

Verification / Alternative check:
Introductory mineral processing texts list washing and sizing under dressing steps specifically used to remove clayey gangue.

Why Other Options Are Wrong:
Calcination/roasting: chemical/thermal changes; do not primarily remove clay films.Smelting: produces molten iron; far downstream of impurity washing.Agglomeration: forms sinter/pellets; occurs after dressing, not before.

Common Pitfalls:
Assuming any heating removes all impurities; clay is best removed by washing and screening before thermal steps.

Final Answer:
Dressing (including washing and hand/mechanical separation)