Process Design

1. MP421 – PROCESS DESIGN | Major Assignment
MP421: PROCESS DESIGN MAJOR ASSIGNEMNT #1
Q1.What types of samples that would be taken to assess for qualitative and quantitative
analysis?
Processing Monzonitic Porphyry Skarn Ore.
1.0.Introduction
Monzonite is an intrusive igneous rock that contains abundant and approximately equal
amounts of plagioclase and potash feldspar; it also contains subordinate amounts of biotite and
hornblende, and sometimes minor quantities of orthopyroxene. Quartz, nepheline, and olivine,
which are occasionally present, produce quartz, nepheline, and olivene monzonites. Monzonite
is not a rare rock type, but it generally occurs in rather small, heterogeneous masses associated
with (and perhaps gradational to) diorites, pyroxenites, or gabbros. (Monzonite. (2008).
Encyclopædia Britannica. Deluxe Edition. Chicago: Encyclopædia Britannica.)
Skarn deposits represent a very diverse class in terms of geologic setting and ore metals. The
term skarn was originally used for the relatively coarse-grained, cala-silicate gangue (garnet +
pyroxene + epidote) associated with magnetic and chalcopyrite deposits. According to
Geology and Mineral Potential in PNG (2005), stated that Several economically significant
Cu–Au skarns are hosted within the thrust faults adjacent to the contacts between intrusives
and limestone… have classified skarn based on mineralogy as follows; Periskarns
(Endoskarns), calcsilicate, massive magnetite and massive sulphide skarns.
Figure 1. Ore body containing Gold rich cap with sulfide mineral increasing in depth.
(Geology and Mineral Potential in PNG, 2005)

2. MP421 – PROCESS DESIGN | Major Assignment
The type of samples used for process design is critical for flowsheet development and process
selection. Therefore regarding the problem statement above, it is stated that due to the
weathering process it has remobilized the copper and iron minerals resulting in gold rich cap,
which it formed both oxide and sulphides of copper minerals. Since the copper ore increases
in depth, the samples taken for qualitative and quantitative analysis will have an impact on the
flowsheet and process design. The top part of the mineralization which mainly composed of
oxide ore will have a different process design and flowsheet compared with the sulfide ores.
Before the actual process design and process selection takes place they is usually the bench-
scale test or the pilot plant test is carried out to determine the mineral characteristics of the
minerals to be processed. The tests carried out qualifies the type of ore and minerals present in
the ore body. There are different ways to assess the samples applying different types of
techniques. The samples that will be assessed for qualitative and quantitative analysis are
through mineralogical assessment and metallurgical test.
1.1.Sampling Type
Diamond Drill/ Core Drill
These are the sampling types were samples are collected by drilling using the diamond
or core drill to remove the core to sample for minerals and they are collected
representatively from the different drill holes. Therefore the first thing happened was
that the skarn ore samples taken for communition and metallurgical testing comes from
the diamond drill. The drill core taken or drilled by the geologist which the core is
splitted and the half is crushed into 13mm for mineralogical assessment and
metallurgical testing.
1.2.Types of Analysis
Mineralogical Assessment
Which is through quantitative analysis, the polished section core will be taken to the
microscope for the Qualitative Evaluation of Minerals by Scanning Electron
Microscopy (QEM*SEM) to analyses the gold and copper present in each size fraction.
The sieve sizes ranges from 53 microns up to 250 microns, therefore when testing
different sizes (250um, 150um, 106um, 75um and 53um) in microscope to determine
the liberation of each sieve size to find out which size fraction will liberated easily from
its gangue and host. Then this size will be regarded as the P80, like for example we say
it would be 75 microns and the ores will be crushed and grinded into 75microns that
will liberate more gold and copper from its host rock and gangue. Therefore the
crushing and grinding machines will be calibrated to that size.
Metallurgical Assessment
It is a qualitative analysis which are performed on potential ore materials to determine
the expected recovery of desired commodity from the ore for a given process and to
determine the characteristic of waste produced by the process and how to mitigate it.
Therefore to analysis qualitatively the ore must be pulverized into too fines and digest

3. MP421 – PROCESS DESIGN | Major Assignment
the monzonite sample with HCl to for acid digestion. To determine the excepted
recovery for each metal present so that it will give the process engineers a detail about
the metallurgy background of the process to be design to produce both the copper and
gold metals.
Q2. How would you prepare the samples?
2. Sample Preparation
Sample preparation is another important part were samples are collected representatively from
the different types of sampling methods. Therefore the first thing happened was that the skarn
ore samples taken for communition and metallurgical testing comes from the diamond drill.
The drill core taken or drilled by the geologist which the core is splitted and the half is used
for mineralogical assessment and metallurgical testing.
For lab test and plant scale test usually the tonnage of samples used for test is normally 10 to
15kg of ore samples. In regards to that, the 10kg of monzonitic porphyry skarn ore from core
drill from different holes has been taken for metallurgical test work to design the plant and
process flowsheet
2.1.Polish Sectioning
The half portion of the diamond drill core taken was crushed into 13mm in diameter for polish
section. The sample was then taken to the rotary splitter to be splitted into as many samples so
that the some can be used in the polish section and liberation analysis (for determining P80
size) using ore microscopy for point counting.
Then it is riffle splitted into the required size so that later it would size using sieve size ranges
from 53 microns up to 250 microns so that it can be easily packed into the small cylinders for
polish section
2.2.Aqua Regia
The splitted samples from the rotary splitter which the head grade is taken for head assay.
It is then pulverized into fines because it will go through acid digestion with HCl in the
fume box. After some minutes the mixture is filtered and the solution is taken for acid
digestion using AAS and some other chemical analysis test.
And samples which will be assessed qualitative would be pulverized and weigh into
500grams for chemical assay. The samples are then digested with HCl acid in the fume box
with a heater. Later the filtrates are removed and the solution are taken for the qualitative
analyses of metal present.
Q3. What information would you require to quantitatively determine the amount of each
mineral present in the ore?
Many metallurgical process act to separate minerals contained in ore. Determination of
amount of minerals in various minerals is often using either the visual estimate recorded

4. MP421 – PROCESS DESIGN | Major Assignment
during geologic logging assumption about combination of elements measured during
chemical assaying, or visual measurement of thin section of core using light microscopy,
however each of this method is subjective. Direct measurement of mineral types is possible
using a technique called Qualitative Evaluation of Minerals by Scanning Electron
Microscopy (QEM*SEM) utilizes a computer controlled scanning electron which can
distingue minerals and their attributes in individual ore particles.
This images can be processed off-line to provide information on;
 modal abundance,
 gain size,
 mode of occurrence,
 liberation characteristic and
 How much of a particular mineral phase may be recoverable.
Therefore to the quantity of each mineral present in the ore, I would measure the proportion
of minerals in the samples, distribution of valuable elements across the minerals,
distribution of deleterious minerals across the minerals, grain size distribution of elements
and particles composition (liberation).
Q4. Discuss the type of processes that would you employ to threat this ore to produce
high purity copper and gold? Illustrate your answers clearly with aid of flowsheet.
3. Introduction
Monzonite is host rock which is made of the plagioclase and silicate mineral within the
earth’s crust. In the problem statement it is stated that the mineral of interest to be extracted
are the gold copper. Since the deposit is a porphyry the mining type will be an open pit.
Pyrite, silicate and carbonate minerals will be treated as gangue and be removed in the tails.
Below is a general flow sheet on how to extract the copper and gold from their ore minerals.

5. MP421 – PROCESS DESIGN | Major Assignment
Figure 4.1: Simplified flowsheet for Cu and Au Processing
3.1.Communition
During crushing and grinding the size of feed is reduced into required sizes for P80 passing
sizes required during plant test. Therefore since gold is riched in the cap of the deposit then
there are course gold in the feed so the crushing and grinding. Communition process
liberate the mineral of interest from their host rock and gangue minerals. So that there is
no more or less crushing and grinding done, if it is too fine more gold and silver will be
lost in the tails and if it’s too fine it will also affect the passing size.
3.2.Gravity Concentrator
Gravity concentration processes rely on the principal that gold contained within an ore
body is higher in specific gravity than the host rocks that contain the gold. Elemental gold
has a specific gravity of 19.3, and for other minerals like copper and the gangues, their
specific gravity ranges between 2-6 s.g. All gravity concentration devices create movement
between the gold and host rock particles in a manner to separate the heavy pieces from the
lighter pieces of material.
Since the gold is course, knelson concentrator is applied to separates the gold from the
rest of the minerals. The course gold are collected at the bottom due to gravity, while
lighter minerals like copper and silver in the slurry passes as overflow to the flotation
Feed
Crushing & Grinding
Heap Leaching Gravity Concentration
Flotation Oxide Ore
Sulfide Ore
Pressure Oxidation
Heap Leaching
Leaching
Solvent Extraction
Stripping/ Electrowinnig
Bullion
Refining
(Au, Ag & CU)

6. MP421 – PROCESS DESIGN | Major Assignment
circuit. The other reason for employing gravity separation is that some of the course gold
will be lost in the flotation cell and might report to the tails and lost.
Figure 4.2: The flowsheet above depicts where gravity concentration is applied for gold
concentration.
The courser gold found in the flotation cell are then sent to the regrinding mill for and then
gravity concentrator is employed to further collect course gold and the overflow passes to
the flotation for copper flotation again.
3.3.Flotation
Froth flotation is a highly versatile method for physically separating particles based on
differences in the ability of air bubbles to selectively adhere to specific mineral surfaces in
a mineral/water slurry. The particles with attached air bubbles are then carried to the
surface and removed, while the particles that remain completely wetted stay in the liquid
phase. Froth flotation can be adapted to a broad range of mineral separations, as it is
possible to use chemical treatments to selectively alter mineral surfaces so that they have
the necessary properties for the separation.
In this circuit we have oxide, sulfide, carbonate and silicate minerals present to float, which
is the gold, silver and copper are the minerals of interest. Therefore to float these minerals
different reagents will be required to float them. And during flotation gangue minerals will
be treated as tails by sending them to the tail dams.
Flotation Sulfide minerals
During flotation, the sulfide minerals which copper, gold and silver contained in it,
will be floated using the anionic collector called the potassium amine xanthate
(PAX). They are the required collector used for sulphide flotation. And the pyrite

7. MP421 – PROCESS DESIGN | Major Assignment
(FeS2) gangue will be depressed by cyanide (CN-
) and later Lime is added to control
the pH to 10.5-11.0 for depressing pyrite and other (unwanted mineral) gangue
mineral whilst floating Gold and Copper.
Pyrite is a combination of iron and sulfur, since the sulfur is harmful to the
environment the sulfide will be floated later and percentage of S present will be
reduce to less than 1% so that it won’t harm the environment and will be dumped
in the tail dump. And locked gold or refractory gold will be recovered later.
Flotation of Oxide Minerals
After floating sulfides minerals, then the oxides are floated using are floated using
sodium oleate which is anionic collector. The low grade oxide minerals will be
treated differently from the sulphides. They will be stored in a dam and apply heap
leaching with sulfuric acid (H2SO4) and left for a month or two and later the solution
will be extracted as solvent extraction.
Oxide ores are low grade ores therefore they are kept or processed differently from
the sulfides. Which is they are heap leached and then solvent extraction is
employed. The solution is electroplated to extract the copper, gold and silver in the
mineral.
Figure 4.3: Flowsheet depicts how to extract low grade oxide ore (Cu, Au & Ag).

8. MP421 – PROCESS DESIGN | Major Assignment
3.4.Pretreatment (Pressure Oxidation)
The methods available for oxidation fall into two categories; hydrometallurgical and
pyrometallurgical. Pyrometallurgical oxidation of sulfide minerals by roasting has been
practiced around the world and it’s thoroughly proven. However due to large production of
sulfide gas to the atmosphere causes pollution and it’s a cost of roasting process.
Hydrometallurgical methods, other than simple preaeration techniques, have been developed
during the past 25 years.
During pretreatment process the sulfide ore will be oxidized from the autoclave, and the
oxygen reliable for oxidation will come from oxygen plant. High content of sulfide in the ore
will be affected in leaching so all sulfide will be converted to oxide, which is capable of
leaching to expose the gold and copper in the ore.
3.5.CIL/CIP
A slurry of ground ore, water and a weak cyanide solution is fed into large steel leach tanks
where the gold, silver and copper are dissolved. Following this leaching process the slurry
passes adsorption tanks containing carbon granules which adsorb the gold, silver and copper.
Sodium cyanide is added to the slurry to dissolve gold, silver and copper forming their metal
and the cyanide complex. The equation below shows the application of cyanide.
During leaching carbon from the CIL/CIP absorbs the gold and silver particles that suspend in
the solutions. The sponges in the carbon is loaded with Au, Ag and Cu metal.
3.6.Solvent Extraction
Solvent extraction processes are employed primarily for the removal of constituents that
would have an adverse effect on the performance of the product in use. An important
application is the removal of heavy aromatic compounds from the solution. Removal improves
the viscosity-temperature relationship of the product, extending the temperature range over
which satisfactory lubrication is obtained. The copper from the CIP/CIL are extracted here,

9. MP421 – PROCESS DESIGN | Major Assignment
which is the gold that is contained in the sponges carbon is extracted from it to further
electrowinning.
3.7.Electrowinnig
The loaded carbon is fed into an elution column where the bullion is washed
off. The barren carbon is recycled. The wash solution pregnant
electrolyte is passed through electrowinning cells where gold, silver and copper are
won onto stainless steel cathodes.
For copper the electrolytes is universally recovered by electroplating pure metallic cathode
copper. Below is what actually happens during copper electrowinning.
Pure metallic copper (less than 20 ppm undesired impurities) is produced at the cathode
and gaseous O2 at the anode.
3.8.Bullion
The loaded cathodes are rinsed to yield a gold and silver bearing sludge
which is dried, mixed with fluxes and put into the furnace. After several

10. MP421 – PROCESS DESIGN | Major Assignment
hours the molten material is poured into a cascade of moulds producing
bars of doré bullion.
3.9.Refining
This process is used to upgrade the products of early recovery processes. The methods
applied to refine Au, Ag and Cu depends on the nature of the materials and amount of
impurities present. Refining is usually performed in two stages:
a. Treatment at the point of production (e.g. at the mine site) to produce a crude bullion
(typically 90% to 99% total precious metals)
b. Refining of crude bullion from the first stage to produce high- purity gold and silver
for sale.
Gold, silver and copper in bullion, they are combined and they can be separated according
to their melting points. For gold the melting point is 1064 °C, silver the melting point is
961°C and for copper its 1723°C. Therefore they can be melted at different temperature
and the mineral of interest would be collected accordingly. And at last Cu, Ag and Au are
recovered at high grade which is economical for this process design.

11. MP421 – PROCESS DESIGN | Major Assignment
Reference:
John O. Marsden & C. Iain House (2006). The Chemistry of Gold Extraction, Society of
Mining, Metallurgy & Exploration.USA.
Anthony.W & Graeme.H (2005), Geology and Mineral Potential in PNG, Alan Caudell
and Assistance Project. PNG.
Bowman, J. R., (1998). Stable isotope systematics in skarns. In: Lentz, D.R. (ed.),
Mineralized Intrusion related Skarn Systems. Mineralogical Association of Canada, Short
Course Series, 26: 99-145.
Monzonite. (2008). Encyclopædia Britannica. Deluxe Edition. Chicago: Encyclopædia Britannica.