Coal washeries: besides clean coal and rejects, what is the name of the additional intermediate-density product commonly obtained?

Introduction / Context:Coal preparation plants separate raw coal into products based on relative density using jigs, heavy media baths, or cyclones. Typical outputs include clean coal (desired low-ash product), rejects (high-ash rock/shale), and an intermediate-density fraction called middlings or middling coal.

Given Data / Assumptions:

• Separation by density/float-sink behavior.
• Three-product arrangement is common.
• Terminology follows standard coal prep practice.

Concept / Approach:Middlings are neither light enough for the clean coal stream nor heavy enough to be rejects. They may be recirculated for re-treatment, blended for appropriate use, or directed to pulverized fuel applications where ash tolerance allows it.

Step-by-Step Solution:Identify three-product split: clean, middlings, rejects.Match the intermediate product term: “Middling.”

Verification / Alternative check:Process flow diagrams for heavy media cyclones routinely show overflow (clean), underflow (rejects), and a controlled cut yielding middlings in multi-stage circuits.

Why Other Options Are Wrong:Concentrate: used in ore flotation, less common in coal prep terminology.Tailing: equivalent of rejects in mineral processing; not the intermediate cut.None of these: incorrect because the standard name is “Middling.”

Common Pitfalls:Confusing coal-prep vocabulary with metallic ore flotation terms (concentrate/tails).

Final Answer:Middling