Thermal decomposition of tetrabromobisphenol-A containing printed circuit boards in the presence of calcium hydroxide

Recycling of printed circuit boards (PCBs) is complicated by the presence of flame retardants containing halogen and phosphorus, as the degradation products of these retardants reduce the quality of the produced gases and liquids. Moreover, during thermal treatment, corrosive and toxic compounds are released and the volatilization of undesirable metals incorporated in the PCB matrix is enhanced. To combat this problem, we investigated the effects of calcium hydroxide (Ca(OH)₂) on the thermal decomposition of both phenol and epoxy resin paper-laminated PCBs containing tetrabromobisphenol-A. Pyrolysis experiments revealed a maximum removal of 94 % HBr, 98 % brominated phenols, and 98 % phosphorus from the gaseous and liquid pyrolysis products. In addition, Br-induced metal volatilization was inhibited, improving the recovery amount in the solid fraction. Thermogravimetry–mass spectrometry revealed that Ca(OH)₂ enhanced the evolution of phenolic compounds produced from the PCB matrix, mainly below 300 °C, while the fixation of brominated compounds took place primarily above 300 °C.