Closed-circuit vs open-circuit grinding:\nCompared with open-circuit operation, which statement about closed-circuit grinding is generally true?

Introduction / Context:
Grinding circuits can run open (mill discharge goes to product) or closed (mill discharge passes through a classifier; coarse returns to the mill). Understanding the qualitative effects of classification—on fineness, size uniformity, throughput, and economics—helps in selecting a circuit configuration for target specifications and energy costs.

Given Data / Assumptions:

• Comparable feed and target limiting size.
• Functional classifier with steady circulating load.
• Similar mill conditions aside from the classifier loop.

Concept / Approach:
In closed circuit, fine particles are preferentially removed as soon as they are generated, reducing overgrinding of fines while forcing additional breakage of coarse particles via recycle. For a given top size, this produces a product with more material near the fine end, increasing specific surface area. It also typically improves size uniformity (contradicting option (b)), increases production at a given limit by avoiding wasted energy on already-fine material (contradicting (c)), and is often more economical (supporting (d)). Among single statements, (a) is a robust, unambiguous truth about closed circuits compared with open circuits.

Step-by-Step Solution:

Verification / Alternative check:
Plant data routinely show higher Blaine/PSSA at the same top size when operating in closed circuit with balanced circulating load.

Why Other Options Are Wrong:

• (b) Wrong: closed circuit tends to improve, not reduce, size uniformity.
• (c) Wrong: production rate is typically higher at a set cut size.
• (d) Often true but can be case-dependent; (a) is the clearest general statement.

Common Pitfalls:
Confusing “higher surface” with “overgrinding”; closed circuits reduce overgrinding of fines by removing them promptly.

Final Answer:
The specific surface area of the product is higher for a given top size limit.