Mineral–Metal Wastes (Bio)/Recycling: Compliance with Circular Economy

This chapter reviews what has been accomplished in metal bio-extraction from so many secondary sources. In some cases, tailings were generated during processing of primary and weathered ores. It has been demonstrated that the use of native microorganisms, naturally present in drainages from mines where sulphide minerals are present, is very attractive in several locations, especially when it comes to the processing of ores with low levels of metals of interest as well as the tailings generated in these processes. In addition, several studies show the possibility of using the mineral substrates remaining in the rocks after such bio-extraction processes, for crops. This is a natural fertilization technique which uses such mineral substrates for augmenting the necessary nutrients for food production, in soils depleted by weathering/leaching or by the inappropriate and intensive use of chemical fertilizers, without affecting the balance of the environment. Following this line of research, there is also a need for technology to recover elements from electronic scraps, bearing in mind that some of them are also used as micronutrients for human beings, especially given the short lifespan of modern electronic equipment. Latterly, electronic waste can encompass dozens of different elements such as base metals, precious metals, rare earth and several heavy metals. Several processes have been used for extracting/recycling those metals. Bearing this in mind, the biotechnological approach plays a pivotal role as a very attractive and cost-effective way for processing such wastes and so many others being dumped in the environment, as natural resources are available in the environment and can be used without much expenses as it is the case of so many microorganisms.