Colloid stability — preventing flocculation: To prevent flocculation (agglomeration of fine particles into flocs), which dispersing agents are most commonly used in aqueous suspensions?

Introduction / Context:In mineral processing, ceramics, and paint formulations, fines tend to agglomerate due to van der Waals forces or charge neutralisation. Dispersants (deflocculants) keep particles apart by enhancing electrostatic repulsion or steric hindrance, thereby stabilising suspensions and improving downstream steps like classification, filtration, or casting. Identifying typical chemical families used as dispersants is essential for troubleshooting slurry behavior.

Given Data / Assumptions:

• Aqueous system of inorganic solids.
• Common, low-cost industrial additives are intended.

Concept / Approach:Alkali silicates (e.g., sodium silicate) and condensed phosphates (e.g., sodium hexametaphosphate, sodium tripolyphosphate) are classic deflocculants. They adsorb on particle surfaces, increase negative surface charge, and raise zeta potential, producing electrostatic repulsion. They also can complex cations that otherwise compress the electrical double layer. Carbonates/bicarbonates are weak pH buffers rather than strong dispersants, while sulphates/chlorides often screen charges and promote coagulation rather than dispersion.

Step-by-Step Solution:

Verification / Alternative check:Ceramic slip preparation and ore pulping practices routinely specify sodium silicate or sodium hexametaphosphate dosages to minimise viscosity rise from flocculation.

Why Other Options Are Wrong:

• Carbonates/bicarbonates: mild pH modifiers; limited dispersing power.
• Sulphates/chlorides: electrolytes that can compress the double layer and induce flocculation.

Common Pitfalls:Overdosing dispersants can reverse benefits by salting-out or altering ionic strength; optimisation by jar testing is recommended.

Final Answer:Silicates and phosphates