Recovery of precious metals from scrap printed circuit boards through pyrolysis

•Precious metals recovery from RAMs and CPUs through pyrolysis.•RAMs pyrolysis product has higher heating values with respect to CPUs.•Precious metals concentrations in the raw material increase after pyrolysis.•4.3 MJ/kg and 2.1 MJ/kg can be recovered from RAMs and CPUs pyrolysis.

Pyrolysis process has many advantages, if integrated in the process of precious metals recovery from scrap printed circuit boards (PCB): the reduction of energy costs during the milling phase, the improvement of dissolution efficiency, the reduction of non-metal residue, low production of dioxins and recovery of bromine. Despite this it is not clear if the process can be sustained burning volatile products (oil and gas). For this reason in the paper pyrolysis tests on samples of central processing units (CPU) and random access memories (RAM) are presented. The pyrolysis of central processing units yielded about 90% of char, 4% of tar and 6% of gas. The pyrolysis of random access memories yielded 82% of char, 9% of tar and 9% of gas. Char energy content was about 4300 kJ/kg for random access memories and 2200 kJ/kg for central processing units, tar energy content was about 29,000 kJ/kg for both, while gas heating value was respectively 20 MJ/kg and 18 MJ/kg. Burning all the volatiles obtained from pyrolysis of random access memories and central processing units, respectively 4273 kJ/kg and 2066 kJ/kg of heat can be obtained.