Heap Leaching Process for Low-Grade Gold Ore Based on High Pressure Grinding Roll Comminution

This heap leaching process for low-grade gold ore based on high pressure grinding roll (HPGR) comminution falls under the technical field of metallurgy, and is implemented in accordance with the following steps:

① The run-of-mine (ROM) gold ore is first subjected to open-circuit coarse crushing, and all coarse crushed products are fed into the secondary crushing system, followed by classification via a vibrating screen. Coarse oversize materials are returned to the secondary crushing equipment for further comminution, while undersize materials with qualified particle size are delivered into the HPGR.

② The HPGR performs open-circuit fine crushing, and the crushed products are treated through the combined operation of a wet vibrating screen and classification equipment. The finer overflow product is fed into the all-slime cyanidation leaching system, while the underflow (settled sand) and coarse-grained materials are mixed with an appropriate amount of lime for alkali adjustment, then transported to the leach pad for heap construction, realizing the classified leaching process for gold ore materials.

③ Upon completion of leaching, gold-bearing pregnant solution and tailings are obtained.

This process adopts HPGR open-circuit fine crushing, whose crushed products feature finer particle size and abundant surface microcracks. It can significantly improve the gold leaching rate, reduce the consumption of leaching agents, and shorten the heap leaching cycle. While the heap leaching operation is carried out, the fine-grained classified products are also recovered simultaneously.

The process comprises the following steps: preparation of a mixed system of sodium iodate, sodium iodide and water; production of complex salts of Au(I) and Au(I₃) under the action of the as-prepared mixed solution and a co-oxidant; extraction of crude gold powder; and purification to obtain refined gold powder.

Compared with the prior art, the gold iodide leaching method adopted in this process significantly improves the extraction recovery and purity of the recovered gold. Meanwhile, the process features simple operation, low environmental risk of the involved chemicals, and low cost, thus reducing production cost and improving production efficiency. Furthermore, iodine can be recycled and reused in the process, which further cuts production costs.

The lead-bearing gold concentrates are treated with the independently developed crystallization washing technology, which enables hydrometallurgical separation of impurities including lead, iron and sulfur during gold smelting and extraction. This process features innovative and unique design, strong adaptability, and wide applicability for refining lead-bearing concentrates (including middlings) obtained from Knelson gravity concentration. It also provides high reference value for the processing of other lead-bearing concentrates.

An increasing number of domestic gold mining enterprises in China have adopted the Knelson gravity concentration process. At present, most Knelson gravity concentrates are processed via pyrometallurgical smelting, which is associated with harsh working conditions and high risk of lead poisoning. The application of this new process can thoroughly address the lead pollution problem, thus filling the domestic gap in this technical field.