Open this photo in gallery: Artisanal miners struggle under the weight of 50 kg sacks of cobalt ore at the Shabara mine in the Democratic Republic of Congo.Siddharth Kara/The Globe and Mail Siddharth Kara is associate professor of human trafficking and modern slavery at Nottingham University and the author of Cobalt Red: How the Blood of the Congo Powers Our Lives. During one of my trips to the Congo, I met Jolie in her small home of cracked brick walls and rusted roofing in the cobalt-mining town of Kolwezi. Although Jolie had invited me to her home that day to…