Rosa Hilda Estrada-Ruiz

Coal is one of the most important sources for energy generation. In order to reach buyer or legislation requirements, and prevent environmental pollution, coal must be washed by processes such as froth flotation to remove mineral matter and to increase the coal quality. Different techniques such as X-ray diffraction and artificial vision are employed to monitor coal flows during the washing process; nevertheless, these techniques require high-cost equipment and qualified personnel to perform the analysis; also, data interpretation is a time-consuming task. The use of non-conventional sensors, such as a solid–liquid electrical conductivity sensor, to forecast the quality of coal offers an easy to employ method to monitor the process in real time, take corrective actions and improve the resulting coal grade, reduce the loss of valuable material and reduce pollution, increasing the sustainability of the process. For this research, coal samples from Región Carbonífera in Coahuila, Mexico were analyzed to obtain their intrinsic characteristics and their electrical conductivity. It was found that the electrical conductivity value is directly proportional to the calorific value and inversely proportional to the ash content. A conductivity value increase from 25 to 30 µS/cm was obtained when using a surfactant modified coal pulp.

Electronic waste stream grows day by day; printed circuit boards are a kind of solid waste that accounts for 6% of electronic waste. When these are discarded, they can cause soil, water, and air contamination; however, if recycled, these can be considered as a secondary source of metals. Physical comminution of printed circuit boards generates particles with sizes smaller than 250 µm, which are typically not included in the recycling process because they are considered as dust and unvaluable; nevertheless, precious and base metals can be found in these particles. The concentration of metals like silver, among others, from these particles can be achieved by reverse froth flotation in a flotation column followed by magnetic separation of the tails products. A mass balance of the flotation column feed, concentrate, and tails indicates that using a pulp modified with 5 ppm methyl isobutyl carbinol plus 5 g/ton oleic acid (both biodegradable reagents), the concentration of the products improved, resulting in recoveries of 86.13 and 13.87% in the concentrate and tails zones, respectively, with a grade of 74.4% in the tails flow. Magnetic separation of the tails product increases slightly the concentration of silver, reaching a silver grade of 74.5%, a recovery amount similar to those obtained employing complex and environmentally unfriendly processes.

A restorative process, where the nonmetallic fraction from e-waste printed circuit boards is reused as a raw material for the conformation of a new polymer matrix composite with increased properties favoring its industrial applications, is proposed with a zero residues approach. Low density polyethylene pellets and nonmetallic fraction particles were mixed, and due to the generation of static electricity during the mixing process, the nonmetallic particles became attached to the polyethylene pellets; the blended material was fed into a screw extruder, producing filaments of the new composite. Mechanical properties increased as the particles content increased, presenting an ultimate tensile strength going from 20 for the raw low-density polyethylene to more than 60 MPa, and a yield strength that goes from 10 to 50 MPa on the composite with 6.0 wt.% particles. Also, the flammability of the composite improved, reducing its linear burning rate and increasing the time between detachment of two consecutive drops. Nonmetallic fraction particles were oriented in the extrusion direction and had a good adhesion with the polyethylene matrix. These composites can be employed for the production of prototypes using additive manufacture.

Nanostructured composites of the aluminum 7075 alloy and carbon-coated silver nanoparticles were synthetized by the mechanical milling technique using a high-energy mill SPEX 8000M; the powders generated were compacted, sintered and hot-extruded to produce 1 cm-diameter bars. The composites were then subjected to a wear test using a pin-on-disc device to validate the hypothesis that second phase-ductile nanometric particles homogenously distributed throughout the metalmatrix improve the wear resistance of the material. It was found that silver nanoparticles prevent the wear of the material by acting as an obstacle to dislocations movement during the plastic deformation of the contact surface, as well as a solid lubricant when these are separated from the metal-matrix