THE IGOLI MERCURY - FREE GOLD EXTRACTION PROCESSERROR: REFERENCE SOURCE NOT FOUND Sidney Mahlatsi, Senior Engineering Technician: Mintek - Small Scale Mining Division ABSTRACT; Mintek has developed a process called iGoli Mercury-free Gold Extraction Process that can be used to extract gold from 0.1 % gold concentrate to produce 99.90 percent gold product. The process uses a mixture of pool acid (dilute hydrochloric acid), bleach (sodium hypochlorite) and sodium metabisulphate to leach and recover gold. Artisanal and small-scale miners concentrate their gold using sluice boxes followed by panning as a final physical separating method. The gold produced in this manner is extracted from the concentrate by a chlorine solution produced from a mixture of pool acid and bleach. The leach liquor contains gold and other metals that are soluble in chlorine media such as base metals and ferrous iron. During leaching excess gas that is produced is redirected to a separate vessel where it is scrubbed using caustic soda to form water and sodium chloride (salt). The slurry from the leaching process is filtered to separate the gold bearing leach liquor and the solid residue. This gold pregnant solution is treated with sulphur dioxide, introduced in the form of sodium metabisulphate, to reduce gold ions in solution to a metallic gold powder. The solid waste produced from iGoli process is rich in silicate with effluent and is neutralized using lime/ limestone with an addition of apatite where necessary to destroy or precipitate all base metals and ferrometals available. The development of this process was mainly driven by the need to ensure reduction in mercury use and subsequent alleviation on the entire biophysical environment. There is an array of mitigating measures that could be used as treatment methods for the safe use of iGoli leaching process. The process wastes which are significantly less toxic are characterized as follows: → Waste solids
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The Igoli Mercury Free Gold Extraction Process Acid Bleach Leaching
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THE IGOLI MERCURY - FREE GOLD EXTRACTION PROCESSERROR: REFERENCE
SOURCE NOT FOUND
Sidney Mahlatsi,Senior Engineering Technician: Mintek - Small Scale Mining Division
ABSTRACT;
Mintek has developed a process called iGoli Mercury-free Gold Extraction Process that can be used to extract gold from 0.1 % gold concentrate to produce 99.90 percent gold product. The process uses a mixture of pool acid (dilute hydrochloric acid), bleach (sodium hypochlorite) and sodium metabisulphate to leach and recover gold.
Artisanal and small-scale miners concentrate their gold using sluice boxes followed by panning as a final physical separating method. The gold produced in this manner is extracted from the concentrate by a chlorine solution produced from a mixture of pool acid and bleach. The leach liquor contains gold and other metals that are soluble in chlorine media such as base metals and ferrous iron. During leaching excess gas that is produced is redirected to a separate vessel where it is scrubbed using caustic soda to form water and sodium chloride (salt).The slurry from the leaching process is filtered to separate the gold bearing leach liquor and the solid residue. This gold pregnant solution is treated with sulphur dioxide, introduced in the form of sodium metabisulphate, to reduce gold ions in solution to a metallic gold powder. The solid waste produced from iGoli process is rich in silicate with effluent and is neutralized using lime/ limestone with an addition of apatite where necessary to destroy or precipitate all base metals and ferrometals available. The development of this process was mainly driven by the need to ensure reduction in mercury use and subsequent alleviation on the entire biophysical environment. There is an array of mitigating measures that could be used as treatment methods for the safe use of iGoli leaching process.
The process wastes which are significantly less toxic are characterized as follows: → Waste solids
Feed → → Waste solution (effluent) → Waste heat → Waste gasesAny potentially hazardous gases released from the gold leaching process are monitored and controlled by neutralization below the legislative requirements. The tailings produced have a high percentage of silica and iron with low levels of base metals. The process is very important to artisanal and small-scale miners as it lowers the risk of mercury poisoning on the miners themselves and mercury pollution into the environment. The process also offers economic benefits because of its high recoveries and product purity coupled with its simple way of waste management. Lastly the process recovers refractory gold which is very difficult to recover using other conventional ASM extraction methods.
1. INTRODUCTION
The environment is a very important part of our lives. It is the complex totality of circumstances
surrounding an organism or a group of organisms, especially the combination of external physical
conditions that affect and influence the growth, development, and survival of organisms.
The natural environment consists of all the conditions affecting the nature of an individual or
community, which we shall never completely understand until we see it as a living organism.
Most of our chemical and mining activities occurring in our every daily life have a significant
negative impact to our environment. In addition, new processes that are developed daily still
impact on the environment either positively or negatively, depending on the type of waste that is
produced by the process.
A process technology has been developed in Mintek for small-scale miners, which uses pool acid,
bleach and metabisulphate to dissolve and recover gold from a gold concentrate. During recovery
the process produces chlorine gas emissions, effluent and solid waste as a generated waste.
2. STUDY OBJECTIVE
A study was conducted in South Africa to derive measures, which could eliminate or minimise
the environmental impacts that might be caused by the implementation of the iGoli process. The
method developed focussed on making the iGoli process environmentally friendly so that the
process can be operated within existing South African legislative standards.
Table 1 and 2 depicts the South African impurity standards within the underground water and the
solid waste generated. The objective of the study was to develop a method, which can be used to
treat iGoli effluent for an effective waste disposal.
Table 1.Limits of the elements in underground water