5. Particle Sizes
http://www.aerosols.wustl.edu/education/AerosolBasics/Size%20range.htm
Theoretical assessment of the source
of acid mist suggests that acid mist is
formed almost entirely from airborne
jet drops and not film drops as
generally understood. Jet drops are
created from the disintegration of a
liquid jet that is formed after the
collapse of the bubble cavity. The
diameter of the jet drops, generated
during copper electrowinning, is
estimated to range from about 0.1
µm up to 54 µm.
http://researchonline.jcu.edu.au/275
30/
pDR 1500
Range
6. Hazards associated with sulphuric acid and its mist
- Short‐term irritation of eyes and skin.
- Nasal problems, throat irritation bronchial hyper reactivity and/or damage to the lining of the throat in the
region of the larynx after repeated exposure to the acid mist (> 0.3 mg/m3).
- Irritation of the lungs (chemical pneumonitis) and upper respiratory tract after brief exposure to high
concentrations of sulphuric acid mist and in severe cases may cause pulmonary oedema.
- Irritant dermatitis (red, itchy, dry skin) and itching due to repeated exposure to low concentrations of mists
or aerosols.
- Etching of teeth after a few weeks exposure, progressing to erosion after a few months exposure.
(NSAA, 2013)
10. Monitoring Methods: Non Selective
Air Pump Filter
System
Detector
Count 7
pDR
MIE 1500
NIOSH 0500
NIOSH 0600
11. The monitoring device:
Nephelometer
Definition:
A nephelometer [1] is an instrument for measuring
concentration of suspended particulates in a liquid or gas
colloid. A nephelometer measures suspended particulates
by employing a light beam (source beam) and a light
detector set to one side (often 90°) of the source beam
12. Brand: Thermo Scientific
Model: pDR 1500
Resolution : 0.1 μg/m3
Particle size range of maximum response : 0.1 to 10 μm
Flow rate range : 1.0 to 3.5 L/min
Aerodynamic particle cut-point range : 1.0 to 10μm, with optional
cyclone accessories
The monitoring device:
Sugested Price: 8,500 USD
15. Physical Barriers: Plastic balls
• It is a most cheapest method to reduce the acid mist
emitions to the environment.
• The fabrication are easy but the use will be strict.
• This method does not produce changes in the other
process but the control of the losses are not easy.
• This element is the best complement to use with a
tensoactive.
19. Mistop®: The natural option
• It is a non-ionic surfactant 100% natural, biodegradable, non-
flammable, non-hazardous, rich in triterpene saponins.
• Made from Quillaja saponaria Mol, (Quillay) tree endemic to Chile.
• This product is formulated to reduce effectively the formation of acid
mist in copper electrowinning processes by reducing surface tension
of the electrolyte.
• This products reduces levels of acid mist, used as a complement to
mechanical barriers, such as polypropylene balls, without producing
adverse effects on solvent extraction or electrowinning processes.
20. How it Work?
• During the process of electrodeposition of copper and its
chemical reaction, oxygen is released into the anodes forming
bubbles
• The bubbles rise to the surface where they coalesce, increase in
size and finally fade, releasing liquid to the environment in the
form of microdroplets that make up the acid aerosol.
• This aerosol forms a fine mist that turns the atmosphere
corrosive, with associated risks, both for physical facilities and
for personnel.
• An efficient way to reduce this problem is by adding surfactants
to lower the surface tension of the electrolyte. This decreases
the force with which the bubbles explode.
• In addition, a thin layer of foam is formed which allows it to
drain back into the liquid medium, thus reducing the formation
of acid mist.
21. Expected results
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2007 2008 2009 2010 2011 2012 2014 2015
100%
52%
56% 54%
37%
45%
62%
59%
Aerosol
Total
Decrease of the total aerosol level with the use of Natural
tensoactive in an electro-winning tankhouse of the great copper
mining industry in Chile
Without Tensoactive With Natural Tensoactive
22. Safety product
• Natural tensoactive has a bounded half life under the operating
conditions of most plants, which ensures that the natural
tensoactive does not accumulate in the system.
61.92
64.77
68.42
64.98
55.17
49.09
57.68
48.91
58.63 58.03
66.61
55.47
40.00
45.00
50.00
55.00
60.00
65.00
70.00
4 6 4 6
220 450
Surface
Tension
(mN/m)
Natural Tensoactive (ppm) | Current density (A/m2)
RECOVERY OF SURFACE TENSION AT RECOMMENDED DOSES AND EXTREME CUR RENT DENSITIES
Mín. de En Estanque Mín. de En Celda Mín. de Descarga
24. Safety product
• Natural tensoactive does not alter the parameters of the
extraction kinetics as the phase separation times, beyond the
values considered as safe.
1
1.5
2
2.5
3
3.5
4
4.5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
PDT
(min)
Different days of Natural and chemical tensoactive dosage
SX Phase Disengagement Time (PDT)
Mistop - PDT (min)
FC 1100 - PDT (min)
25. Safety product
• The product is safe for the processes and for people in general.
28. Thanks for your attention
amarchant.ing@gmail.com | +569 68594645
Editor's Notes
Good afternoon, everyone,
As I was introduced by Matthieu, my name is Alvaro Marchant and I am a technical consultant for DKC, specifically for their product Mistop and its application in Mining. I have more than 10 years of experience in the use and application of Quillaja extract and more than 8 years specifically dedicated to the application of Mistop in electrowinning. In the following talk I will present the product, its uses and advantages and then answer some questions.
You are all welcome.
I will not refer to the chemical formation of oxygen bubbles in the electrolyte matrix but will talk a little about the phenomenon through which acid mist forms in the environment.
Some bubbles reach the surface, in the way indicated in the figure on the left, and the disruption on the surface generates some small drops, that normally fall back into the liquid. Most of them when they reach the surface they burst like soap balls, releasing many micro-drops. These micro-droplets are so low in weight that they remain suspended over the cells and are then carried away by air currents inside the plant, thus forming the acid mist.
The size of the micro-droplets is important because according to several studies these would be between 0.1 and fifty-four microns.
The health problems that are associated with particulate material are particularly concentrated in the 2.5 micron particles, so the most dangerous fraction of micro-droplets is the smallest, which can penetrate deep into the lungs and cause a lot of damage.
Sulphuric acid is a strong acid and will oxidise, dehydrate or sulphonate most organic compounds. Dehydration occurs because sulphuric acid has a strong affinity for water. It forms various hydrates when is in contact with organic matter or water vapour. Although it is miscible with water, contact with water generates heat and may produce a violent reaction.
Sulphuric acid mists have long been recognised as having the potential to cause the following health effects (NSAA, 2013):
Knowing how micro-droplets are produced and the nature of this phenomenon, we will review some of the most common ways to measure and monitor acid mist.
In the high-precision selective method used in official H&S-related standards measurements, a sample of plant air is pumped through a filter that retains several particles. This filter is transported under a strict protocol to a certified laboratory, where it is analyzed in an Ion Chromatograph. This apparatus is capable of identifying the compounds in the sample and defining exactly the amount corresponding to sulfuric acid. The disadvantage of this method is that it takes time and if there is no equipped laboratory on site, the results of the analysis can take days. This is not useful for making day-to-day operational decisions.
The selective reference method is one of the most used due to its low cost. In this system, an air sample is passed through a pump and bubbled into an indicator solution. When equilibrium is reached, the indicator turns color and the analyst records the time.
The analyst compares the time with a formula and obtains a value for the sulfuric acid in the sample.
The disadvantage of this method is that the reaction time can be in hours as well as in minutes. The method is very sensitive to concentration peaks, which can result in significant errors.
The non-selective method consists of a pump, a filter and a detector. Unlike the other methods, this system counts all the particles that pass through the detector. It does not distinguish between acid and dust.
This method is based on the well-founded assumption that in an acid mist environment the majority of the particles in the environment are acid particles. There are references that indicate that at least 60% of what the method measures corresponds to sulfuric acid.
The great advantage of this method is the response time because measurements are obtained in real time and this facilitates day-to-day decision making.
The equipment that uses the non-specific method is a nephelometer and DKC uses this particular equipment to do the in-plant monitoring.
The equipment is robust and only requires one annual calibration.
Now that we have seen how acid mist is formed, what is the size of its particles and what are the ways to measure them, we will see the most efficient ways to control it.
The most widespread forms of control are physical barriers used in conjunction with surfactants
The function of this physical barrier is very simple, but with high importance.
This product will be used in almost 3 layers, more than 4 layers are unnecessary.
The first layer covers the electrolyte surface in almost 65%, then the surface of the electrolyte in direct contact with the environment decreases dramatically.
The second and third layers become like a seal. The microbubbles that pass through the second layer only advance until the third layer.
A little percent of the bubbles generated will be free to the environment in consequence, the acid mist will be decreased.
We will now talk about a specific product that turns out to be the option to replace FC1100 in most tasks.
How it work
During the process of electrodeposition of copper and its chemical reaction, oxygen is released into the anodes forming bubbles
The bubbles rise to the surface where they coalesce, increase in size and finally fade, releasing liquid to the environment in the form of microdroplets that make up the acid aerosol.
This aerosol forms a fine mist that turns the atmosphere corrosive, with associated risks, both for physical facilities and for personnel.
An efficient way to reduce this problem is by adding surfactants to lower the surface tension of the electrolyte. This decreases the force with which the bubbles explode.
In addition, a thin layer of foam is formed which allows it to drain back into the liquid medium, thus reducing the formation of acid mist.
In this slide we can see a reduction of the constant acid mist over time of about 50%. These measurements are made on the basis of a system with the use of spheres in the cells for both the "no-surfactant" case and the others.
Mistop is safe for SX as it is largely degraded in the electrowinning process.
In this sheet you can see the surface tension measurement taken in the same process at different locations (in the feed tank, in the cell and at the cell outlet).
It can be seen that the surface tension tends to be largely recovered.
The degradation process of Mistop results in other saponins with lower active tension and residual soluble sugars.
The phase separation time (PDT) is largely unaffected which allows for continuous operation without major problems.
The recommended dosage is based on the safety of this parameter.
No mortality or visible effect on behaviour was recorded for any of the test species, so no tests were conducted at intermediate concentrations to determine LC50
The product Mistop, can be considered " Innocuous - Not Toxic "
We have finished this presentation and I hope that you now have a clearer idea about the product, the way it works and the safety it offers for processes, people and the environment.
I am open to any questions you may have or doubts that may remain. These can be asked now or later directly to my contact media. (email and whatsapp)
