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Analytical Methods

Ring pulveriser

Antech offers Fire Assay, Atomic Absorption Spectroscopy and Cyanide Leach analysis to clients.  A brief desciption fo each method is found below.  More details are given under Services

Sample Preparation

Prior to analysis, sample preparation is carried out.  Sample preparation varies with the sample type but for most samples consists of drying and size reduction by crushing and grinding.  Rock samples are dried in ovens at 100ºC.  The dried samples are crushed to - 6 mm size in a jaw crusher.  The crushed sample is then ground to better than 90% passing 75 micron in a steel ring grinder.  Antech uses grinders with a 4 kilogram capacity which means the most samples are ground in their entirety which produces a more representative analytical split.

"One of the keys to our success is the emphasis and investment we place in sample preparation size." - Jeremy Elliott, General Manager

After pulverisation, a split of the sample is analysed by one or more method.  Antech offers Fire Assay, Atomic Absorption Spectroscopy (AAS)  anad Bottle Roll (cyanide leach) analysis for rocks, soils and sediment samples.  

Fire assay

Fire assay is the most common gravimetric method for the analysis of gold and silver and can also be used for Platinum Group Elements (PGE)

The method consists of the digestion of the sample by mixing the sample with lead oxide (litharge) and other fluxes such as sodium carbonate, borax, silica and potassium nitrate.  The sample plus flux mixture is fused in a furnace.  The fusion process reduces the litharge to molten lead and the silica to a borosilicate slag.  The gold and silver in the fused material collect in the molten lead.  The lead and slag are separated after cooling and the precious metals separated from the lead by cupellation.  The remaining gold and silver are weighed in a micro balance to determine the precious metal concentration in the original sample.

Fire assaying is a labour intensive process requiring highly skilled technicians.  Antech's assayers are among the most experienced in southern Africa.

Atomic Absorption Spectroscopy (AAS)

In AAS analysis the sample is dissolved into solution, referred to as "digestion" and the solution is then drawn into a flame in order to atomize the contained elements.  Concurrently light from a hollow cathode lamp is passed through the flame during atomic absorption occurs.  The reduction in intensity of the light beam is measured and correlated with the concentration of the target elements in the sample solution.

The quality of an AAS analysis is wholly dependent on the quality of the sample digestion.  The most common method of sample digestion prior to AAS analysis is Aqua Regia Digestion.  This method consists of treating the sample with a 3:1 mixture of hydrochloric and Nitric acids and heated.  This method effectively dissolves sulfides and other refractory materials.  Antech offers hot aqua regia nad other digestions methods depending on the client's needs.

The AAS analytical method can be combined with the fire assay digestion process to produce low level gold analysis know as Fire Assay-Atomic Absorption or FA-AAS.  In this process the borate bead produced by Fire Assay digestion is itself digested in Aqua Regia and the solution analyzed by AAS.  Antech offers the FA-AAS method to clients as well as standard flame AAS.  This method is appropriate for geochemical samples.

Antech has a GBC Avanta and two 932 machines operated by trained and experienced personnel.

Bottle roll (cyanide leach)

The Bottle Roll method is used to determine amount of gold in a sample which can be extracted by leaching with cyanide solution, also known as "cyanide extractable" gold.  This method is used in mineral process control and in the metallurgical assessment of exploration samples.

In the bottle roll method split of the prepared sample is placed in a glass container with dilute cyanide solution and agitated on a roller for 24 hours.  The gold content of the cyanide solution is then analyzed by AAS.  For process control samples will cyanide concentrations and leach times similar to those of the operating or proposed plant.