The ore which cannot be concentrated by froth floatation process is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → CaCO3
Froth floatation is used to concentrate sulphide ores. The powdered ore is mixed with water, a collector (pine oil, fatty acids, xanthates) and a froth stabiliser. The collector makes the sulphide mineral particles non-wettable by water, so they stick to the oil-coated air bubbles and rise with the froth, while the gangue is wetted and sinks.
Option (1) CaCO3 — Cannot be concentrated by froth floatation. It is a carbonate, not a sulphide; its particles are wetted by water and do not come up with the froth.
Option (2) ZnS — Concentrated by froth floatation. Zinc blende, a sulphide ore of zinc.
Option (3) HgS — Concentrated by froth floatation. Cinnabar, a sulphide ore of mercury.
Option (4) FeS2 — Concentrated by froth floatation. Iron pyrites, a sulphide mineral.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Froth Floatation Method – “This method has been in use for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water. To it, collectors and froth stabilisers are added.”