Metal content determination is one of the critical aspects of preparing electronic waste for metal recycling. In spite of the fact that end-of-life printed circuit boards are considered to be a secondary resource reservoir, no standard procedure exists for determining the total metal content in this heterogeneous multicomponent material containing plastics, metals, alloys and ceramics. We investigated the utilization of United States Environmental Protection Agency (US EPA) microwave acid digestion (Method 3052) and various modifications of this procedure for effective releasing of Cu, Fe, Ni, Pb and Zn from waste printed circuit boards (WPCBs) from mobile phones. The maximum contents of Cu (22.6 wt.%), Fe (5.0 wt.%), Ni (2.0 wt.%) and Zn (2.6 wt.%) were obtained using the standard (unmodified) US EPA 3052 digestion procedure, but the total digestion of PCB material was not achieved. The solid residue material after digestion by means of the US EPA 3052 method consisted predominantly of oxides (Ca, Mg and Al) and fluorides (Ca and Mg), and some particles contained minor amounts of Fe and Cu.

Various types of waste, including dusts, are produced in the pyrometallurgical production of copper from secondary raw materials. According to the European Waste Catalogue and Hazardous Waste List, dusts from secondary copper production are classified as hazardous waste. In secondary copper production 3.87 million tons of copper were produced worldwide in 2017. The dusts are produced in the following thermal operations: reduction of the melt in the shaft furnace (shaft furnace dust), converting (converter dust), and pyrometallurgical refining (refining dust). These dusts contain significant amounts of heavy metals (Zn, Pb, and Sn) in oxidic forms. The dusts are regarded as secondary raw materials, and it is necessary to look for ways of extracting these heavy metals. The aim of this work was to characterize the individual types of dust and determine their quantitative and qualitative composition. The content of heavy metals in copper shaft furnace dust is (52.16% Zn, 19.33% Pb), in copper converter dust (32.40% Zn, 14.46% Pb), and in refining dust (32.99% Zn).

Fine-grained fraction (<1.25 mm) of industrial zinc ash was characterized in terms of chemical and phase compositions as well as leaching behaviour in hydrochloric acid solutions. Waste product contained about 55% Zn, 14% Cl, and less than 0.4% of other metals (Fe, Pb, Al, etc.). It was a mixture of metallic zinc, simonkolleite, zinc oxide, and zinc hydroxide chloride. Dissolution of metals from the zinc ash was determined depending on the solid-to-liquid ratio (1:80-1:20), acid concentration (0.23-2.0 M), and temperature (20-60ºC). The best results (almost 100% zinc recovery) were obtained for 2M HCl at 20ºC, S:L ratio 1:20, and leaching time 30 min. The final solutions were contaminated mainly by iron and lead ions (both below 0.15 g/L). Further treatment of the solution to obtain metallic zinc or zinc chloride was also proposed.