Process for recycling precious metals from waste materials at the Brinston plant

Johnson Ma Jie Chemical Co. scrap precious metals recovery plant, located in the northern suburbs of London Brin Youngstown, put into operation in October 1979. The Brinston plant not only recovers precious metals from various waste materials with high efficiency, but also recovers precious metals from primary raw materials (including electrolytic anode mud, etc.). The process of recycling precious metals from various raw materials is shown in Figure 1. Similar to the plant's process, there is a process used by the US Bureau of Mines to recover gold. The operations of these processes include all conventional processes for precious metallurgy, but the control of the production process is advanced.

Figure 1 Process flow of waste precious metal recycling at the Brinston factory

First, the pre-treatment and classification of incoming materials

Although the conventional method of fire-electrolysis is mature in the process of recovering gold and silver from waste raw materials, the sources of waste raw materials are wide, the types are complex, and the grades are very high (from a few tenths to ninety percent). Therefore, the primary problem is to pre-process and classify used raw materials to ensure the accuracy of sampling analysis. Then, according to the type and grade of the raw materials, the most suitable treatment method is selected. Otherwise, the production process will increase and the production cost will increase.

The pretreatment of the raw materials includes incineration, drying, grinding, sieving and mixing (or melting), and then sampling and analysis. These processes are carried out according to the form and type of raw materials, and not all raw materials must be processed through these processes ( See Table 1). Such as wet powder and fine mud, just dried in steam water jacket drying furnace, hot air fluidized layer drying furnace or electric hot plate drying oven. Waste materials containing organic materials (plastics, etc.) and other combustibles (oils, etc.) are usually burned in a muffle furnace. The air is cleaned by static electricity or a bag filter to ensure that the precious metal does not lose with the smoke. Ceramics, crucibles and refractory materials, as well as dried or incinerated materials, are ground by a continuous ball mill that is continuously screened and periodically emptied. Small batches of raw materials are milled with a grinding disc. The main control parameter for grinding is the grinding size. For lean ore, a suitable particle size is -30 mesh. Since the bulk material discharged from the mill is usually a metal block, in the process of pre-treatment of the incoming raw materials, it usually includes grinding the material for sampling and recovering the metal block from the work. That is, the finely divided fine particles are separately sampled and the recovered metal blocks are melted and sampled. In order to improve the environment and eliminate noise, there is a soundproof room in the mill room.

Table 1 Pretreatment and sampling analysis of waste materials

Second, sampling and analysis

Mixing blade iron fines on the concrete floor, then sampled with a cone stack quartering or riffling quarter method. However, since the fine-grained material often contains -30 mesh metal particles, it is easy to cause segregation error of the grade. To this end, the United Kingdom and the United States have designed the following new sampling system.

In the UK, a complete set of automatic sampling systems is used in each standard silo for grinding, sieving, sampling, storage and transportation. The system feeds the -30 mesh fine ore into a large container with inclined rotation. The mixed fine ore is fed into the shuttle feeder through the vibrating feeder, and then fed into the horizontal rotating collection box to ensure that the fine ore is evenly distributed from the sampling system. Flow out. This system has proven to be a versatile sampling system suitable for a variety of fine-grained materials, including poorly flowable powders.

A new sampling system recently designed in the United States is to pass the sieved fine ore through two vertical spiral mixers, then into a saddle-shaped two-way sampler, and take each of the powder mines flowing from both sides. A sample containing 1% of the total. The two comparative samples were respectively ground by a vibrating mill and then analyzed by shrinking in a rotating grid-like sampler to ensure that the samples were truly representative.

The laboratories at the Brinston plant are equipped with equipment for fire test and gravimetric analysis, as well as state-of-the-art instruments such as atomic absorption spectrometers, X-ray fluorescence spectrometers and electronically controlled direct reading emission spectrometers. Product quality is subject to rigorous analysis and testing.

Third, the melting and refining of raw materials

The raw materials which were pretreated and sampled were selected according to the smelting and refining process of Table 2 according to the level of precious metals and other components.

Table 2 Smelting and refining processes of raw materials