Magnetic separation applicability: which mineral among the following is generally not treated by magnetic separation?

Introduction / Context:
Ore beneficiation relies on differences in physical properties. Magnetic separation exploits magnetic susceptibility contrasts. Knowing which minerals respond to magnetic fields is a frequent exam topic in mineral processing.

Given Data / Assumptions:

• Low to high-intensity magnetic separators are available.
• Minerals listed: rutile (TiO2), galena (PbS), chromite (FeCr2O4), siderite (FeCO3).

Concept / Approach:
Galena (lead sulfide) is effectively non-magnetic; beneficiation typically uses froth flotation and gravity techniques. Chromite is strongly paramagnetic and separable in high-intensity magnetic fields. Siderite (iron carbonate) and some titanium minerals (rutile exhibits weak paramagnetism) can show measurable response in specialized magnetic separators, though rutile is more commonly separated electrostatically in practice.

Step-by-Step Solution:
Identify magnetic susceptibility: galena ≈ diamagnetic/negligible.Others exhibit paramagnetic behavior or contain iron enabling magnetic response.Select galena as not subjected to magnetic separation.

Verification / Alternative check:
Processing routes for lead ores emphasize flotation over magnetic methods, confirming galena’s unsuitability for magnetic separation.

Why Other Options Are Wrong:
Chromite: routinely beneficiated magnetically.Siderite: iron-bearing; magnetic upgrading possible after roasting or in high-intensity fields.Rutile: weakly paramagnetic; although often separated electrostatically, magnetic susceptibility exists, so “not subjected” fits galena best.

Common Pitfalls:
Equating common industrial route (electrostatic for rutile) with impossibility; the question asks which is not subjected at all—galena.

Final Answer:
Galena