Refractory gold and silver ores present significant challenges because precious metals are encapsulated within sulfide matrices, severely limiting extraction by conventional cyanidation. In this study, a pyritic concentrate from the Bacis Mine (Durango, Mexico) was characterized and subjected to two oxidative pretreatments—roasting and alkaline pressure oxidation—before cyanidation. X-ray diffraction confirmed pyrite to be the dominant phase, with quartz and minor carbonates contributing to the material’s refractory character. Roasting at 550 °C achieved gold and silver extraction of 80% and 70%, respectively, which improved to 89% Au and 74% Ag with the addition of hydrogen peroxide. In contrast, alkaline pressure oxidation at 150 °C and 1 MPa O₂ yielded the highest extraction of 92% for Au and 76% for Ag at 1 h. Thermodynamic analysis using the Fe–S Pourbaix diagram at 80 °C supported these experimental results, showing the destabilization of FeS₂ under oxidizing and moderately alkaline conditions. Overall, this study demonstrates that alkaline pressure oxidation is a technically efficient and environmentally favorable pretreatment for refractory gold ores.

Twenty-five years ago, to stimulate economic growth, Mexico encouraged foreign-owned companies to build facilities, maquiladoras, along the border for production and assembly of products for export to the United States. The passage of NAFTA made it easier for U.S. companies to build these facilities and now 60% to 70% of the maquiladoras are U.S. owned. Unfortunately, as pointed out by Jose Bravo of the Southwest Network for Environmental and Economic Justice, Few follow U.S. or Mexican environmental law, therefore, unsafe and unhealthy working conditions, hazardous waste dumps, contaminated water, and uncontrolled contamination from industrial facilities dominate life in most border towns [Schmidt, 2000]. Heavy metal contamination exists in aqueous waste streams of industries, including metal plating facilities, industrial operations that involve the processing of ferrous and non-ferrous metals. Some metals associated with these activities are Cd, Cr, As, Pb and Hg. This are not biodegradable and tend to accumulate in living organisms, causing various diseases and disorders. The purpose of this research is to investigate the use of a novel method for the minimization of toxic metals in the wastewater from the México–U.S. border region. A very promising electrochemical treatment technique, which does not require chemical additions, is Electrocoagulation (EC). This operates on the principle that coagulation of contaminants from an aqueous medium is caused by the combined effects of electrolysis gases (H2 and O2) and the electrolytic production of cations from iron and aluminum anodes that corrode during electrolysis. This study reports on the products of EC as part of an effort to explore the parameters that can be most effectively manipulated to improve the overall process. Understanding the fundamental mechanisms of electrocoagulation will allow the design of more effective wastewater treatment processes.

At the start of 2025, newly imposed tariffs—particularly those threatened by the U.S.—have significantly impacted global gold and silver mining production. In Mexico, extractive metallurgy plays a vital role in recovering these and other metals (including copper, lead, and cadmium) from ores, with applications ranging from magnetic materials to high-tech industries. The electronics sector is the largest consumer of gold and silver, using approximately 80% of gold in microchips and semiconductors. Beyond electronics, gold serves as an efficient catalyst in fuel cells and solar panels, enhancing energy conversion. In conventional Merrill-Crowe operations, precious metal precipitates often suffer from low quality due to co-precipitation of impurities like arsenic, copper, and especially lead, which increases zinc dust consumption, flux requirements during smelting, and shortens crucible lifespan. To address this, the present study proposes a hermetically sealed leaching process using sulfuric acid to selectively remove lead and copper. Following leaching, a barren solution undergoes gravity-driven nucleated precipitation in a serpentine reactor, employing sodium sulfide as a reducing/precipitating agent and sulfuric acid for pH control. Experimental results indicate that pH critically influences the removal efficiency of zinc and copper cyanide complexes. Optimal removal occurs at pH 7–9.5 for zinc and pH 2–4 for copper, achieving up to 99% elimination of these cyanide species. Furthermore, over 90% of cyanide bound in copper, lead, zinc, and iron complexes was recovered. Using natural hydroxyapatite to treat the pregnant cyanide solution effectively removed residual copper and lead ions, yielding a high-purity doré product with 99% precious metal content.