Chapter 7 Multiple Choice Questions

* not completed

. Select the correct statement about rare earth ores from the list below.

La is found only in monazite and bastnaesite. correct incorrect

Xenotime does not contain Ce. correct incorrect

Ce is the major lanthanoid component of bastnaesite and monazite. correct incorrect

Pm is found in bastnaesite, monazite and xenotime. correct incorrect

* not completed

. Consider the following statements about ion exchange chromatography for separation of the f-elements.
(i) The affinity of the ion exchange resin for Ln³⁺ decreases with decreasing Ln³⁺ radius.
(ii) The affinity of the ion exchange resin for Ln³⁺ increases with decreasing Ln³⁺ radius.
(iii) The affinity of [HEDTA]^3- for Ln³⁺ decreases with decreasing Ln³⁺ radius.
(iv) The affinity of [HEDTA]^3- for Ln³⁺ increases with decreasing Ln³⁺ radius.
(v) Small Ln³⁺ are eluted from the column before large Ln³⁺.
(vi) Large Ln³⁺ are eluted from the column before small Ln³⁺.
Now select the correct statement below.

(i), (iii) and (v) are correct. correct incorrect

(i), (iv) and (v) are correct. correct incorrect

(ii), (iv) and (vi) are correct. correct incorrect

(ii), (iv) and (v) are correct. correct incorrect

* not completed

. Consider the following statements about sources of the actinoid elements.
(i) The major known deposits of U are in Australia
(ii) The major known deposits of U are in Kazakhstan.
(iii) U and Th always occur together in natural deposits.
(iv) Th occurs mainly alongside lanthanoid elements.
(v) The main source of Np is reprocessed nuclear fuel.
(vi) Cm and Pu occur together with U in natural deposits.
Now select the correct statement below.

(ii) and (iii) are correct. correct incorrect

(i), (iv) and (vi) are correct. correct incorrect

(ii) and (iv) are correct correct incorrect

(i), (iv) and (v) are correct. correct incorrect

* not completed

. Lanthanoid metals are produced industrially by

reduction of LnF₃ with Ca correct incorrect

electrolysis of aqueous solutions of LnCl₃ correct incorrect

electrolysis of molten LnPO₄ correct incorrect

thermal decomposition of Ln₂(C₂O₄)₃ correct incorrect

* not completed

. Consider the following statements about the solvent extraction process for separation of the lanthanoids.
(i) The strength of binding of the extractant to Ln³⁺ decreases with decreasing Ln³⁺ radius.
(ii) The strength of binding of the extractant to Ln³⁺ increases with decreasing Ln³⁺ radius.
(iii) The extractant forms a neutral complex with Ln³⁺.
(iv) The solvent extraction process results in concentration of small Ln³⁺ in the organic phase
(v) Stripping of Ln³⁺ from organic to aqueous requires a lower pH for La³⁺ than for Yb³⁺.
(vi) Stripping of Ln³⁺ from organic to aqueous requires a higher pH for La³⁺ than for Yb³⁺.
Now select the correct statement below.

(i), (iii), (iv) and (v) are correct correct incorrect

(ii), (iii), (iv) and (vi) are correct correct incorrect

(ii), (iii) and (v) only are correct correct incorrect

(i), (iv) and (vi) only are correct correct incorrect

* not completed

. Rare earth elements always occur as mixtures in their ores. Select the incorrect statement below.

For each tonne of Nd that is extracted from monazite, approx. 4 tonnes of Ce is also extracted. correct incorrect

For each tonne of Eu that is extracted from bastnaesite, approx. 330 tonnes of La is also extracted. correct incorrect

For each tonne of Yb that is extracted from xenotime, approx. 5 tonnes of Ce is also extracted. correct incorrect

For each tonne of Lu that is extracted from xenotime, approx. 3 tonnes of Ce is also extracted. correct incorrect

* not completed

. Consider a gas centrifuge with a separation factor of 1.15. How many stages are required in order to enrich natural abundance ²³⁵UF₆ (0.7%) to 3.5% for use in a nuclear reactor?

11 correct incorrect

9 correct incorrect

13 correct incorrect

12 correct incorrect

* not completed

. Prior to reprocessing, spent nuclear fuel rods are normally stored in water for up to a year because

radioactivity of fission products generates heat correct incorrect

fission of ²³⁵U continues for up to a year correct incorrect

the initial fission products are long lived correct incorrect

minor fission products can be extracted into the water correct incorrect

* not completed

. The PUREX process achieves separation of U and Pu by

treatment with C₂O₄^2- to precipitate Pu(C₂O₄)₂ correct incorrect

extraction of a mixture of U(VI) and Pu(IV) with a solution of (BuⁿO)₃P=O correct incorrect

reduction of U(VI) to U(III) so that it is no longer coordinated by (BuⁿO)₃P=O correct incorrect

reduction of Pu(IV) to Pu(III) so that it is no longer coordinated by (BuⁿO)₃P=O correct incorrect

* not completed

. Consider gas diffusion, gas centrifuge and laser methods for isotopic enrichment of uranium. What is the order of decreasing energy costs of these three methods?

Laser > Gas centrifuge > Gas diffusion correct incorrect

Gas diffusion > Gas centrifuge > Laser correct incorrect

Gas diffusion > Laser > Gas centrifuge correct incorrect

Gas centrifuge > Gas diffusion > Laser correct incorrect