Chapter 21, Problem 1RQ

Summary Introduction

Rusticyanin is a kind of copper protein. Rusticyanin is present in the periplasmic membrane of the Acidithiobacillus ferroxidans. These bacteria are seen in pyrite deposits that are rich in iron sulfur minerals. These bacteria oxidize iron and sulfur as the energy source and therefore, used in bio-hydrometallurgy industry.

Explanation of Solution

Covellite (CuS) is a general, insoluble form of copper ore that is present in nature. The sulfur component present in the CuS is oxidized to sulfate by Acidithiobacillus ferroxidans releasing the copper part as cupric form or Cu²⁺. The crucial step is carried by A. ferrooxidans in indirect oxidation of copper is given below.

$\text{CuS}+{\text{2O}}_2\to {\text{Cu}}^{2+}+{\text{SO}}_4{}^{2-}$

In addition, spontaneous oxidation of covellite by ferric ion also releases cupric form. The ferric ion is obtained from the oxidation of FeS₂ that is also catalysed by A. ferroxidans. Using the scrap iron, the copper metal is recovered from the solution. The reaction can be given as:

${\text{Fe}}^{\text{0}}{\text{+Cu}}^{\text{2+}}\to {\text{Fe}}^{\text{2+}}\text{+}{\text{Cu}}^{\text{0}}$

The temperature progressively increases inside the leaching dump that affects the iron-oxidizing microbes. A. ferroxidans is a mesophile that is unable to survive at high temperature and so it is outcompeted to some extent by thermophilic chemolithotrophs that are also iron-oxidizing in nature and thrives above 30°C. Some chemolithotrophic iron oxidizers are Leptospirillum ferroxidans and Sulfobacillus. In temperature ranging between 60 to 80°C Sulfobacillus species are seen predominantly.