Insights Into Differential Biomining Traits of Indian Copper Sulphides
Total Page：16
File Type：pdf, Size：1020Kb
COMMENTARY Insights into differential biomining traits of Indian copper sulphides Sharadindra Chakrabarti and Ranen Sen Metal solubilization in microbiological Sulphobacillus sp., Acidithiobacillus fer- nantase and H2SO4 at pH 1.5–1.9 was leaching of copper sulphides is promoted rooxidans, Acidithiobacillus thiooxidans considered. Licananbutase lipoprotein, by synergism of microbe consortium. sp., Acidithiobacillus caldus, Acidithi- an active agent of Licanantase, is obser- Low-grade copper sulphides (chalcopy- obacillus ferridurans and Acidithiobacil- ved in secreted protein fractions of At. rite, pyrite) in India, when subjected to lus ferrivorans, whereas Archaea ferrooxidans and At. thiooxidans. The in- bacterial leaching/biomining in acidic includes Acidianus sp., Ferroplasma sp., itial fractions of 3.5–30 kDa indicate an medium show differential responses. Metallosphaera sp. and Thermoplasma increment in copper recovery. The rea- Such reaction occurs due to geological/ sp. Till today, species of Acidithiobacil- gent contains 5–99% of Licanantase geochemical environments of ore forma- li – At. ferrooxidans, At. thiooxidans, At. lipoprotein along with 1–95% H2SO4 at tion. The co-existence/symbiotic interac- ferriphilus, At. albertensis, At. ferrivo- pH 0.8–3.0. In India, working pH ranges tions of bacterial species along with P–T rans, At. ferridurans, At. sulfuriphilus between 1.4 and 1.9, depending on ore conditions are equally responsible for and At. caldus – are observed. The most specificities. The above reagent has to be their characteristic behaviour. Igneous influential metal bioleaching microbes added at a concentration of 0.01– activities associated with formation of are At. ferrooxidans and At. thiooxidans. 100 mg/l. For ores of four deposits Singbhum (Jharkhand)–Malanjkhand (Mad- Microbial leaching can be direct or in- worked with, the concentration was of hya Pradesh) copper deposits influence direct1. At. ferrooxidans and At. thioox- higher order, varying from 70 to 80 mg/l, the rate of bioleaching of refractory chal- idans are capable of catalysing oxidation whereas Licanantase lipoprotein was copyrite. This rate is higher in sedimen- of reduced sulphur compounds (sulphide, around 87% with 90% H2SO4. tary remobilized deposits of Khetri– elemental sulphur, thionates, etc.), gene- In chalcopyrite–pyrite-dominated low- Rajpura Dariba–(Rajasthan) Ambamata rating sulphuric acid as the final product. grade ores of India, copper recovery (Gujarat). It is found that microbes han- Both these bacteria reduce sulphite and improved by around 9–11%. The Chilean dle leaching problems within genetically thiosulphate as intermediate products experts, however, claimed a progress of defined abilities. that directly/indirectly solubilize metal- up to 20%. World over, 80% copper is produced associated sulphides. This lowers the Molecular genetic studies of Acidithi- through conventional processing (crush- formation of passivating substances on obacilli are time-consuming because of ing, grinding, floatation, fusion-conver- reactive ore surfaces, oxidizing elements long generation time, low yields in liquid sion of concentrates, electrolytic directly by transferring electrons from media and poor growth on solid media. refining). However, this is limited to ore to biomass. At. ferrooxidans can So was earlier accumulated in low-tem- high-medium grade ores, specificities of catalyse oxidation of Fe2+ to Fe3+ that perature bioleaching of chalcopyrite and ore deposits and processing plants. There strongly oxidizes sulphides/other com- associated ores with psychrotolerant pure are none-the-less valuable, relatively pounds whose oxidation is required. and mixed cultures, primarily causing low-grade resources which are sub- Dopson et al.2 expressed doubts about passivation of copper surface. Studies on economic and remain unexploited for the incapability of organomixotroph Fer- microbial ecology of bioleaching till date lack of effective technology. However, roplasma strains to fix carbon dioxide. have relied primarily on standard tech- these ores could be recovered through Leptospirillum, as member of the bio- niques of molecular genetics, especially recent developments in microbial ecology leaching consortium, is providing them in the spatio-temporal distribution of and metabolic processes of biomining/ with fixed carbon3. microorganisms in heap bioleaching. bioleaching, using tools of comparative Bioleaching of Indian ores describes Presently, emerging fields of compara- genomics/metagenomics/bioinformatics. heap bioleaching in acid medium tive genomics and metagenomics have Complete genomic sequences of Acidi- (H2SO4) at pH 1.4–3.5. Incorporating se- broadened our understanding of microbial thiobacillus ferrooxidans and Acidithi- lected biomass with increased oxidizing ecology and metabolic processes of bio- obacillus thiooxidans have led to a better property has been attempted. However, it leaching. understanding of biochemical pathway is difficult to maintain selectivity in Bioinformatics of the genome seque- predictions and physiology of iron– Indian heaps. Increasing heap tempera- nce of At. ferrooxidans has led to several sulphur oxidation for higher copper solu- ture to 50°C to accelerate bioleaching is metabolic regulatory models; some were bilization. impractical for cost constraints. Organic validated in part through experimental Low-grade copper in chalcopyrite of carbon is further added to improve studies like sulphur and iron uptake and Malanjkhand–Khetri–Amba–Mata–Sing- the rate of leaching; but cost nullifies assimilation4,5, carbon metabolism6, etc. bhum may be subjected to bioleaching implementation possibilities. Another Comparisons on a large scale of genomes through direct/indirect microbial actions. impending factor is maintaining carbon addresses fundamental questions, such as Microbes essential for biomining belong under varying heap conditions, because the number of functional genes, identifi- to the bacterial domain of Archaea, that of specificities of ore of a particular cation of species-specific genes, distribu- are acidophilic and chemolithotrophic. region. tion of genes among functional families, In biomining, there are bacteria of For improvement in heap bioleaching etc. Functional abilities of bacteria are Acidiphillium sp., Leptospirillum sp., as executed in Chile, addition of Lica- in fact limited by genomic characters. 1812 CURRENT SCIENCE, VOL. 120, NO. 12, 25 JUNE 2021 COMMENTARY Recent reports7 on Sulfobacillus thermo- lite-granodiorite of early Proterozoic tamination in the copper belt of Ghatsila. sulfidooxidans, At. ferrooxidans and At. age10. The Amba–Mata deposit is a stra- At. ferridurans has similarities with the caldus reveal how the extent of functional ta-bound exhalative sedimentary deposit, gene sequence of At. ferrooxidans; hence abilities depends on genomic attributes. metamorphosed11. Copper mineralization it was earlier incorrectly identified as At. Comparative genomics helps consolidate in Khetri–Kolihan belt is sedimentary– ferrooxidans. gene identification. For example, in iron diagenetic, later remobilized and meta- The whole genome sequencing of oxidation specific to At. ferrooxidans, morphosed12. different Acidithiobacilli species has the potential genetic differences between Various members of the consortium, provided new insights into variegated various Acidithiobacillus species are proactive in leaching, form separate clus- functions. Until now nine At. ferroox- combined to develop evolutionary mod- ters and may or may not be mutually in- idans strain genomes are available15. At. els of the respective genomes and mutual teractive at the initial stage of heap ferrooxidans observed in Indian deposits species interactions (ecophysiology). If bioleaching; but, as the exothermic reac- has not been genetically analysed. Hence leaching problems (which bacteria can- tion proceeds, members of the consor- it is unknown whether it is a variant not handle alone) are visible, the process tium become mutually interactive. strain. At. ferrooxidans IO-2C genome16 needs to be complemented by additional Leaching operations under the Iron has shown significant genetic variants of leaching abilities of bacteria and Arc- Mountains (Northern California, USA) over 75,000 variants. In Indian mines, it haea. The case of Licanantase lipoprote- metagenomic project have, however, is not known which variant and gene ins, discussed earlier, is a pointer. added more comprehensive understand- functions (like iron and sulphur metabol- Bioleaching experimentation at labora- ing of heap bioleaching13. Heap bio- ism, nitrogen fixation, heavy metal resis- tory/pilot/commercial scales in dumps/ leaching proceeds in three stages. It tance, etc.) we are dealing with. The rate heaps have been done over three dec- arises from temperature increase due to of leaching is dependent on gene func- ades. In the late 1980s, the first copper exothermic biological oxidation of (Fe tions. Comparison of genomes addresses dump leaching was attempted at Khetri. II) and S°. An early stage of leaching basic questions such as the number of However, it did not work due to impro- is found at 30–40°C by mesophilic functional genes, identification of spe- per leaching pad design. In the early organisms such as At. ferrooxidans, At. cies-specific genes, distribution of genes 1990s, copper heap/dump leaching- thiooxidans and Sulfurisphaera. As tem- among functional families, mechanisms cementation plant was established indi- perature