الطرق الحديثه فى معالجة الذهب Eng. Ayman El-Amin

• Physical processes o crushing and grinding • Chemical processes o chemical breakdown of ore to enable the extraction of gold

PROCESSING Physical processes Chemical processes reduce the size of the ore rocks, and include steps such as crushing and grinding. are those that separate the metal from the other components within the ore rocks.

The ore is passed through a three-stage crushing circuit and then through the grinding mill to reduce the size of the ore (physical processing). The gold is recovered from the ore by leaching, elution, and then via the electro winning cell (chemical processing).

CRUSHING & GRINDING The purpose of crushing and grinding the ore rocks is To reduce the size and to allow the valuable minerals to be separated from those that are of no value. (Small-sized particles of ore provide a greater surface area on which the chemical processes can act to extract gold).

CRUSHING & GRINDING The end product must be very fine to allow the greatest surface area of the rock to be covered by the solution that will assist in the recovery of gold. Any oversized rocks are screened out and will not pass on to the next stage of treatment of the ore. They pass back either to the secondary or tertiary crusher to be put through the crushing process again.

Heap leaching The choice between these methods depends primarily on the relationship between particle size and recovery, capital and operating costs, and the dissolution rate in each case .An example of the relationship between particle size and gold recovery for two different ore types sometimes other factors, such as the recovery of other metals of value (i.e., silver platinum group metals [PGMs]), environmental considerations, and availability of capital financing may play an important role in this

Column Leach Tests

Stacking to heap

Irrigation

Pond

Heap leaching flow sheet

CIL Carbon is added in leach so that the gold is adsorbed onto carbon almost as soon as it is dissolved by the cyanide solution. The CIL process is frequently used when native carbon is present in the gold ore.

المعالجات الكيميائية باضافة السيانايد إلى الخليط, و ذلك لإذابة جزيئات الفلز (الذهب) من صخور الخام التي تم تكسيرها.

أشهر املاح السيانيد Sodium cyanide (NaCN) Potassium cyanide (KCN) Calcium cyanide [Ca(CN2)]

عادة لا يزيد pH عن 11 زيادته ترفع من كمية السيانيد الحر في المحلول. سيانيد الهيدروجين HCN و السيانيد الحر بامكانها أن تتأكسد بوجود الأكسجين لتشكل السيــــــــانات (CNO-) و التي غير مرغوب فيها لاعاقتها عملية الاذابة للذهب.

The dissolution of gold takes place via the following reaction: REACTANTS PRODUCTS 4 Au + 8 CN + O2 + 2 H2O ------> 4 Au(CN)2 + 4 OH

Gold + Free Cyanide + Oxygen + Water  Gold Cyanide + Hydroxyl

عوامل تؤثر على معدل التفاعل الكيميائي الأكسجين: بوجود كمية كافية من الاكسجين في المحلول نحصل على عائد أكبر من الفلز (الذهب) و زمن أقصر في العملية - تركيز السيانيد: pH عادة في الحدود بين 01 الى 12 الحرارة: زيادة الحرارة تزيد معدل الانحلال و ايضا تقلل محتوى الأكسجين في المحلول حجم الحبيبات: متوسط حجم الحبيبات المطحونة عادة يعتمد على الدراسة المجهريه الضغط: