Pemurnian emas skala kecil dengan Zinc precipitation &

Gold cathodes

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Pengantar• Operasi tambang emas memperlakukan batuan tambang dengan

sianidisasi kemudian logam mulianya direkoveri dari larutan pregnant dengan Zinc Dust ( proses Merryl Crowe ) atau karbon aktif dan elektrowinning. Operasi besar smelting untuk mengolah zinc precipitasi atau cathodes dalam upaya untuk mendapatkan produk campuran emas dan perak (Bullion). Bagaimanapun operasi yang sederhana tidak menjamin produk finalnya disebabkan batasan nilai ekonomi dan teknis. Oleh karen itu, disini dijelaskan proses untuk mengekstrak dan memurnikan emas anda.

• Mempertimbangkan aspek yang dipertimbangkan diatas, tujuan presentasi berikut untuk menunjukkan kemungkinan penggunaan proses pemurnian tanpa investasi modal yang besar seperti proses2 pemurniaan yang biasa digunakan di workshop perhiasan logam.

1.KANDUNGAN ZINC PRECIPITATES

• A zinc precipitate can have a chemical composition like this: 12% gold, 5% silver, 12% CaO, 20% Cu, 11% Zn, 5% Zinc. The process involves the following stages

2. Langkah perlakuan precipitasi zinc

• Perlakuan dengan asam nitrat.

• Precipitasi perak .

• Pelarutan emas dengan aqua regia.

• Precipitasi emas.

2.1.Perlakuan dengan asam nitrat

is leached with hot nitric acid so that can be dissolvedsilver and common metals. Then, the slurry is filteredand the residue is washed with hot water. The resultdepends mainly of nitric acid dosage and temperature.The next table shows some possible result

2.2.Precipitasi perak• The obtained silver nitrate solution is treated with sodium

chloride in order to precipitate silver as silver chloride. The reaction is shown below

• NaCL + AgNO3 = AgCl + NaNO3• The amount of silver in the solution from acid leaching can

be calculated by simple calculation. Now, it is necessary know the addition of sodium chloride. For this must be considered the following rule of thumb: each gram of silver in solution requires 0.55 grams NaCl.

• The silver chloride precipitated is filtered and washed with distilled water, after, must be transferred to a beaker for its treatment with zinc dust which has been previously acidified lightly with sulphuric acid. The metallic product obtained is filtered and washed with hot distilled water. The final product is dried and finally smelted in order to get metallic silver.

2.3.Pelarutan emas dengan aqua regia

• The precipitated obtained in Step (a) is leached with hot aqua regia (85 – 90 oC). The amount of aqua regia to be employed must be in excess (at least 100 times) to the required theoretically. The reaction is shown below.

• Au + 3HNO3 + 4HCl = HAuCl4 + 3NO2 + 3H2O• After attacking with aqua regia will be added urea

which decreases the residual HNO.• 6 HNO3 + 5CO(NH2)2 = 8N2 + 5CO2 + 13H2O• The slurry is filtered and the residue is washed

with hot distilled water until eliminate a yellowish coloration in the filtered solution

2.4.Pengendapan emas• Metallic gold is precipitated from the solution obtained in

step (c) by adding sodium bisulphite. In theory, each gram of gold needs 1.89 grams of sodium bisulphite. However, must be added more, approximately 1.5 more times.

• 2HAuCl4 + 2NaHSO3 = 2Au + 4HCl + Na2SO4 + SO2• The gold precipitated is filtered and washed with hot

distilled water and an ammonium solution. Finally is dried and smelted. The smelting process can be done with borax, silica and saltpeter for one hour to 1100 oC.

• There are alternative reagents to sodium bisulphite such as oxalic acid, sulphurous, acid and sulphur dioxide. The cost of treating zinc precipitated can be in the range 8 to 12 dollars/Kg zinc precipitated.

• With this treatment gold recovery is higher than 98% and the impurities are almost imperceptible because the obtained gold is practically pure, 995 to 999 fine.

3.Perlakuan terhadap katoda emas

• Steel wool cathodes need a previous treatment with hot hydrochloric acid in order to dissolve all the metallic iron. The residue obtained is filtered and washed with distilled water. Then, the residue will be treated with aqua regia as was described in the previous steps for zinc precipitates.

Flowsheet for each treatment