TECHNIQUES OF MET ANALYSIS

fire assay

most widely accepted classical method for determining gold and silver content in ores, concentrates, and metallurgical products

fire assay

high-temperature analytical technique used to separate and measure precious metals

selective collection of precious metals

precious metals can be selectively collected into another metal (lead), instead of staying mixed with the waste minerals

Reduction

converting metal oxides into pure metal produces molten lead

charge

complete mixture of materials placed into the crucible before heating (fusion)

smelting

process of melting everything together so the sample separates into two liquid layers

metal layer

lead + precious metals

slag layer

waste minerals

compositions of charge

ore sample, fluxes, litharge, reducing agents

collector metal

molten lead

lead

gathers and concentrates precious metals into one small button

separation of metals into a lead collector

Gold and silver have a strong ability to dissolve into molten lead

lead button

at the end of the smelting, a solid piece is obtained

final purification through cupellation

after collecting gold and silver in lead, next step is to remove the lead

cupellation

purifies the precious metals by removing lead through oxidiation

cupel

a porous cup where lead button is heated

litharge

lead oxidize

dore bead

gold and silver do not oxidize easily, so they remain behind as a small shiny metallic bead

sample preparation and weighing

ensures that the sample tested is representative and accurately measured

fusion and smelting

break dw=own the ore and separate valuable metals from waste materials

fluxes

weighed sample is mixed with chemicals

litharge

lead collector

borax

slag former, lowers melting point

soda ash

basic flux, neutralize silica

silica

acidic flux, balances basic ores

flour/carbon

reducing agent

slag

waste minerals combine with fluxes

lead button formation

concentrates gold and silver into a small mass for easier recovery

cupellation to produce dore bead

removes lead and leaves behind only gold and silver

parting and weighing of au/ag

separates gold from silver and allows precise measurement

parting

chemical pricess used to separate gold from silver after cupellation

inquartation

metallurgical process used in fire assay where silver is intentionally added to a gold-containing alloy so that the final alloy contains at least 3 parts silver to 1 part gold

inquartation

addition of silver to gold before acid parting so that nitric acid can dissolve the silver and leave pure gold behind

slag

molten glass-like waste material formed during smelting

slag calculations

important to prepare correct fusion charge

slag calculations

help assayer determine the correct proportions of fluxes to produce a slag that is fluid, stable, and chemically balanced

silica, metal oxides, borates from borax

compositions of slag

acidic slag

contains excess silica, rich in acidic oxides, more viscous, may trap precious metals if not balanced

basic slag

contains excess basic oxides, mroe fluid and corrosive, may attack crucibles

basicity ratio

important concept used to describe chemical balance of slag, it tells us whether slag mixture is more acidic or basic

BR is < 1

Acidic slag

BR is > 1

Basic slag

basic

high carbonate or iron oxide

acidic

high silica

scorification assay

type of fire assay which ore samples is melted in an open dish

scorifier

an open dish where ore sample is melted

scoria

During heating, base metals are oxidized and absorbed into a slag-like layer

scorification assay is useful for samples that contain high amounts of

base metals

bullion assay

analytical process used to determine purity and precious metal content of bullion, which refers to metallic products such as Gold bars, Silver bars, Doré bullion (impure gold-silver alloy from mining), and Smelter or refinery intermediate products.

solution assay

analytical method to determine concentration in a liquid solution rather than in solid ore or bullion

classical assay methods

provide accurate baseline results, used in remote mining sites with limited instruments, support metallurgical process control, and help determine ore value feasibility

iodometric titration and gravimetric

traditional methods in copper assay

high industrial values

copper is commonly analyzed because of this

gravimetric sulfate and volumetric method (EDTA titration)

lead assay methods

Complexometric titration, gravimetric oxide, electrolytic assay

Zinc Assay Methods

Permanganate Titration Method, dichromate titration method, gravimetric method

Iron assay methods

iron

one of the most abundant metals and important in steel production

zinc

widely used for galvanizing and alloy production

lead

important in battery manufacturing and smelting industries

1. sampling

2. sample prepartion

3. dissolution or decomposition

4. separation of metal

5. measurment

6. calculation and reporting

basic steps in metal assay

gravimetric

weighing precipitate

volumetric

titration and volume reading

electrolytic

weighing deposited metal

modern analytical instruments

provide faster results, higher sensitivity, and improved reliability, which are essential in industrial decision-making and quality control.

spectrophotometry

measures how much light a substance absorbs at a specific wavelength, commonly used to determine metal ions in ores and industrial samples, such as Iron (Fe), Copper (Cu), Zinc (Zn), Nickel (Ni), and Lead (Pb)

spectrophotometry follows

beer-lambert law

Providing rapid quantitative analysis

Detecting low concentrations of metals

Reducing human error through automation

Allowing multiple samples to be tested efficiently

advantages of spectrophotometry

Xray Diffraction

analytical technique used to identify crystalline phases in minerals and metals.

XRD follows

Bragg’s Law

Xray Flourescence

used to determine the elemental composition of a sample.

accuracy, efficiency, decision-making, industrial competitiveness

role of modern analytical instrumentation

Sample must be in solution form so light can pass through and absobred

spectrophotometry principle

Works only on crystalline solids, not solutions. Fine particle size = better diffraction

XRD principle

Analyzes elemental composition directly (solid, powder, or pellet)

XRF principle

Mylar film

thin, transparent polyester film (polyethylene terephthalate, PET) used as a window or cover for powdered samples in X-ray Fluorescence (XRF).

pellet die

a steel mold assembly used to compress powdered samples into a solid, flat pellet for analysis.