Manufacturers, disassemblers and brokers are shipping tons of low grade electronic scrap to recover gold and silver contained in it. As better and better product design and plating technology develop, the intrinsic value of this material tends to decline. It is important to employ efficient and accurate methods of determining the precious metal content of these materials. Reduced costs and increased returns can be accomplished by using good analysis, segregation and preparation of material to be refined. Basically charge varies with the type of material can be processed separately and individually. There will be no comingling of the material with other different material and 100% of the material will be processed.
Because of the sliding weight scale, many people think their returns can be maximized by lumping all types of electronic scrap together into a single shipment. This may or not be so depending on the nature of the material. Each material type must be evaluated on the basis of specific charges which apply and segregated or combined accordingly. In this way, materials that are vastly different in makeup should not be combined. For instance, do not combine circuit boards with plated pins free of plastic. Differences in processing methods dictate these two materials are best handled separately. Large amounts of base metals or plastic only serve to drive up your treatment charges since they return no precious metals value to the batch. It is important to evaluate removal of the excess weight by comparing removal costs against the processing costs per kilo. It is important to keep in mind the factor in salvage value of the steel, aluminum or other material to remove.
The main objective of processing plants is to homogenize and sample the material for precious metals determination. Since electronic scrap usually contains fiberglass, plastics or other combustion materials, the first step is to remove these materials. This operation can be accomplished through a carefully controlled, environmentally safe incineration process which is known as thermal reduction. Once the material has been burned, the resulting ash must be taken, complete with metal and ceramic components in order to grind them. The objective is to reduce the particle size to a specific point where a representative sample can be taken. Since a portion of the material is metal, it is difficult to reduce all the material. Then, all of the milled material is passed over a separator to remove larger metal pieces from the resulting fine powder portion and set aside.
As the ground ash material is being separated, the powder portion is being collected. Once the entire lot has been ground and sieved, the powder portion is ready for sampling and is loaded into mixers designed for this purpose. After mixing thoroughly to ensure homogenization, a representative sample is taken. The material is weighed and the weight recorded for use in determining the precious metal content of the charge. The metallic portion is must be processed differently to ensure a representative sample sine the sizes and makeup of the different metal components are all unique. In order to do this, the metallic portion is melted in an induction furnace capable of reaching 1540 oC. Each lot is evaluated before melting to determine if copper needs to be added as a solvent for the various metals. Certain metals are immiscible when melted together and such segregation would not allow a homogeneous sample. Once the material in entirely liquid, the material is stirred with a special rod and a molten sample taken. The material is poured into ingots and after cooling enough to solidify, but while still not, each ingot is stamped with a processing number to prevent loss of identity. Again the weight of the bars is recorded for determining the actual precious metal content.
All samples are sent to the lab for assays. Upon assay completion, a precious metal determination is made by calculating the content of the powder and the content of the bars and adding them together. A final settlement statement and check is performed.