Why is it expensive to extract copper from a contaminated land where the percentage of copper is low, using the traditional method?

It is expensive to extract copper from a contaminated land where the percentage of copper is low using the traditional method because the said method is energy extensive. Energy is a big portion of the cost in any plant. Having a contaminated land means that there are many waste elements than the useful portion of the land. Extracting the useful part requires more energy which results to higher costs.