Filter aids in solid–liquid separation: which of the following materials is NOT commonly used as a filter aid in industrial filtration?

Introduction / Context:
Filter aids are inert, porous powders used to build a highly permeable precoat or to body-feed a slurry, thereby preventing blinding of the filter medium and improving clarity and cycle time. Typical industrial filter aids include diatomaceous earth (kieselguhr), perlite, and processed cellulose. This item checks recognition of what is and is not a standard filter aid.

Given Data / Assumptions:

• Focus is on common, proven filter aids for pressure or vacuum filtration.
• Goal is to identify the option that is not generally employed as a filter aid.
• Applications include syrups, oils, fine inorganic slurries, and beverages.

Concept / Approach:
The ideal filter aid is chemically inert, low density, porous, and available in controlled particle-size grades. Diatomaceous earth and purified wood cellulose meet these criteria. Asbestos historically served as a filter aid/precoat (though now restricted for health reasons). Raw rice husk is not a standard graded filter aid; while rice husk ash can be a silica source, untreated husk lacks the controlled permeability and safety/qualification data normally required.

Step-by-Step Solution:
List common filter aids: diatomaceous earth, perlite, processed cellulose, (historically) asbestos.Evaluate each option against that list.Conclude that rice husk is not a standard industrial filter aid.

Verification / Alternative check:
Manufacturer datasheets for precoat and body-feed products consistently list DE, perlite, and cellulose grades; rice husk does not appear as a qualified filter aid.

Why Other Options Are Wrong:
Asbestos: historically used (now discouraged), but it is indeed a filter aid.Diatomaceous earth: the most common filter aid.Purified wood cellulose: widely used as a low-density filter aid and precoat stabilizer.

Common Pitfalls:
Confusing agricultural by-products with engineered filter aids; performance depends on graded porosity and inertness.

Final Answer:
Rice husk