2.7.4. Synthesis of Acid chloroauric trihydrate (HAuCl4.3H2O)

Fig. 8d shows the block flow diagram to produce HAuCl₄.3H₂O, which starts with the mining and extraction of gold (Au) from the ore. The process to convert Au into HAuCl₄.3H₂O was described by Gross [14]. Firstly, Au is diluted in aqua regia (75% HCl, 25% HNO₃) to produce HAuCl₄ according to Eq. (8). However, a side reaction takes place between HCl and HNO₃ (Eq. (9)). The reaction between Au and aqua regia is highly exothermic. Therefore, heat was assumed to be 0 and no energy source is required. Besides, water consumption was estimated according to the methodology process showed by Gross [14].