Sinhon thiourea | Gold extraction by thiourea method

Thiourea, also known as thiocarbamide (CAS No.: 62-56-6), has a molecular formula of SCN₂H₄, is a white, shiny rhombic hexahedron, tastes bitter, has a density of 1.405 g/cm3, is easily soluble in water, and its aqueous solution is neutral. Sulfur has low toxicity, is non-corrosive, and does no harm to the human body. Sulfur can dissolve gold, which has been confirmed by experiments. In the presence of an oxidant, gold is transferred into the thiourea acid solution in the form of Au(SCN₂H₄)²⁺ complex cations. Thiourea gold dissolution is an electrochemical corrosion process, and other chemical equations can be expressed as follows:

Au+2SCN₂H₄=Au(SCN₂H₄)+2 +e

Choosing a suitable oxidant is the key issue of thiourea acid gold dissolution. The more suitable oxidants are Fe3- and dissolution, so the chemical reaction formula of thiourea gold dissolution can be expressed as:

Au+2SCN₂H₄+Fe³⁺-Au(SCN₂H₄)+2 +Fe²⁺

Au+1/4O₂+H⁺+2SCN₂H₄=Au(SCN₂H₄)+2 +1/2H₂O

The precious liquid obtained by thiourea gold dissolution can be used for gold precipitation by iron, aluminum replacement or electrolytic deposition according to the amount of gold it contains, and the gold mud is dissolved to obtain the gold. The gold mud dissolution process is the same as that of cyanide gold mud.

The leaching rate of thiourea gold dissolution mainly depends on factors such as medium pH value, oxidant type and dosage, sulfur dosage, mineral composition and gold particle size, leaching temperature, leaching time and gold leaching process. Thiourea is unstable in alkaline solution and easily decomposes into sulfide and aminocyanide. However, thiourea is relatively stable in acidic medium. Therefore, considering the stability of thiourea, dilute sulfuric acid solution of thiourea is generally used as a leaching agent when thiourea gold is extracted, and it should be noted that acid should be added first and then thiourea to avoid excessive local temperature of the slurry and make thiourea hydrolyzed and ineffective. The acidity of the medium is related to the concentration of thiourea. The acidity decreases with the increase of sulfur concentration. Under normal temperature and sulfur dosage conditions, the medium pH value should be less than 1.5, but the acidity should not be too large, otherwise it will increase the acid solubility of impurities.

Thiourea gold extraction is a new non-toxic gold extraction process. Many countries in the world have adopted this method to treat gravity gold concentrate and flotation gold concentrate.

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