Progress, Challenges, and Perspectives of Bioleaching for Recovering Heavy Metals from Mine Tailings

Table 3

Count, centrality, and earliest occurrence year of keywords.

Count	Centrality	Year	Keywords
26	0.10	2009	Bioleaching
10	0.15	2009	Iron
10	0.05	2010	Heavy metal
10	0.31	2009	Acidithiobacillus ferrooxidan
8	0.20	2011	Bacteria
7	0.10	2012	Extraction
7	0.12	2009	Copper