In the tranditionally way, after the CIL or CIP gold ore processing plant produce the gold deposition on the cathodes of electrowinning cell,  the cathodes are removed from the cell for calcining and smelting. During smelting the calcined cathodes are heated in a gas-fired furnace to a molten state in the presence of slag-forming fluxes. The slag captures the impurities and floats upon the molten gold. The entire furnace charge is then poured into moulds, resulting in doŕe gold bars ready for sale. On average, a doré bar contains 50-75% pure gold. These bars require further refinement before the metal can be used as raw material for producing gold items.

So if the mining company directly sale the doré bar. The price is relatively low compared with Gold bullion.

In order to solve this problem and create more profit for the gold mining company, ZJH minerals adopt hydrometallurgy to Extract Pure Gold and Silver from gold deposition produced by electrowinning cell. By this method, the mining could directly sale the pure gold and silver bar.

Please refer to the follow project case in Sudan.

hydrometallurgy to Extract Pure Gold and Silver from gold deposition produced by electrowinning cell

Project objective: CIL plant is expected to produce 25 kg gold deposition by the electrowinning cell each time, reserving twice the capacity space, and designing the smelting target of 50kg for each batch. After purification, more than 98% gold purity standard is reached, which is convenient for market saling. The silver contained in the gold deposition was recovered and purified, reaching the standard of 98% Ag bar.

Process flow diagram

ZJH hydrometallurgy to Extract Pure Gold and Silver from gold deposition produced by electrowinning cell

Extract Pure Gold from gold deposition produced by electrowinning cell

 

Process description

The raw material of this project is the gold deposition from the elution and electrowinning process. After the gold deposition generated  is transported to the workshop by transport vehicle, it is transported to the steel platform by electric hoist and upper hopper, and added to the reaction kettle by feeding shovel.

Nitric acid impurity removal

Nitric acid is a strong oxidizing and corrosive acid. When using nitric acid to remove impurities from coarse gold, impurities such as Ag, Cu, Pb, Zn and Fe in coarse gold react with nitric acid and enter the liquid phase. Gold remains in the solid phase.

The purpose of nitric acid impurity removal includes two aspects: one is to obtain higher gold grade, less slime material; On the other hand, silver and other precious metals are separated to facilitate subsequent recovery.

Precipitating silver by NaCl

Silver is dissolved in nitric acid and enters the liquid phase. The filtrate is transferred to PE bucket and sodium chloride is added. Silver ions in the solution can combine with chloride ions to form silver chloride precipitation. Most base metal chlorides dissolve in water, which separates and concentrate silver from most base metals. After settling the silver, use the filter pan to filtrate it.

Ag+ + Cl- = AgCl↓

Zinc powder replacement

Silver chloride can be easily replaced by active metals into metallic silver under certain conditions. After the reaction is completed, the silver chloride filter slag is transferred to PE bucket, and hydrochloric acid is added to make a slurry. The silver is replaced by zinc powder, and excess zinc powder is removed with dilute hydrochloric acid.

Zn + 2AgCl =Ag + ZnCl2

Gold ingot

The gold deposition after impurity removal and the silver powder after replacement are dried in the baking pan and gas furnace (provided by the owner), and then cast in the medium frequency gold smelting furnace, which is equipped with 5kg gold ingot mold and 5kg silver ingot mold.

Gold bar and silver bar produced by hydrometallurgy to Extract Pure Gold and Silver from gold deposition