Ball and tube mills charged with flint or porcelain media are typically selected for size reduction of which materials, to avoid iron contamination and achieve fine grinding?

Introduction:
Media choice in tumbling mills affects contamination, product purity, and wear. Flint or porcelain (ceramic) balls are used when iron pickup must be minimized, such as in ceramics and certain non-metallic mineral applications.

Given Data / Assumptions:

• Ball/tube mills with non-metallic media (flint/porcelain).
• Goal: fine grinding with minimal iron contamination.

Concept / Approach:
Grinding media can shed material into the product. For whitewares, glass, feldspar, quartz, and other non-metallics, iron contamination is detrimental (color/chemistry). Hence, non-metallic media are chosen. Asbestos is fibrous and not efficiently ground this way; rubber is not normally size-reduced in such mills; limestone grinding for cement typically uses steel media due to throughput and cost.

Step-by-Step Solution:
Identify applications needing low iron: ceramics, glass batch, non-metallic ores.Match to media: flint/porcelain provide low contamination.Conclude correct selection is non-metallic ores and ceramic raw materials.

Verification / Alternative check:
Industrial practice and handbooks list porcelain-lined mills with flint pebbles for feldspar, silica, kaolin, and glaze preparation to preserve whiteness and purity.

Why Other Options Are Wrong:

• Asbestos: fibrous; milling behavior and health concerns make it unsuitable.
• Rubber: elastomeric; typically not comminuted this way.
• Limestone for cement: steel media is standard for economy and throughput.
• Metallic concentrates: steel media acceptable; minor iron pickup is usually not critical.

Common Pitfalls:
Assuming “any” ball mill uses any media; the chemistry of the product dictates media selection to control contamination.

Final Answer:
Non-metallic ores and ceramic raw materials