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Properties - Sulphuric
Acid - Acid Quality
March 12, 2003
Introduction
The quality of acid is
often defined in terms such as commercial grade, technical grade, electrolytic grade,
battery grade, food grade, etc. These terms
are general in nature and may differ from supplier to supplier and from country to
country. The way to get around this ambiguity
to have national standards that define the physical properties and maximum levels of contaminants permissible in
various grades of acid. In the United States grades of acid are defined in the Federal
Specification and by the FDA in the Food Chemicals CODEX.
Ultimately it is the
purchaser that defines the quality of acid that is produced and sold while complying with
the applicable regulations and standards (i.e. food industry).
| Component |
Typical Ranges |
Federal Spec
(Note 1) |
Comments |
| Ammonium |
NH4 |
< 10
ppm |
10 ppm |
- |
| Antimony |
Sb |
< 1
ppm |
1 ppm |
- |
| Arsenic |
As |
< 0.1
to 1 ppm |
1 ppm |
Smelting of ores
containing arsenic will result in off-gases containing arsenic. |
| Beryllium |
Be |
- |
- |
- |
| Cadmium |
Cd |
< 0.5
ppm |
- |
- |
| Chloride |
Cl |
< 1
to 50 ppm |
10 ppm |
Smelting of ores
containing chlorine compounds will result in off-gases containing HCl. Removal of HCl in the gas cleaning system
depends on equilibrium conditions in the scrubbing circuit. Chlorides may also be present in makeup water
used in the gas cleaning system and as dilution water. |
| Chromium |
Cr |
< 1
ppm |
- |
Chromium can be
present in smelter off-gases or result from the corrosion of stainless steel piping and
equipment. |
| Copper |
Cu |
1 to 50
ppm |
50 ppm |
Copper is present in
the smelter gases as a dust. Proper design
and operation of the gas cleaning system will control the amount of copper reporting to
the product acid. |
| Fluoride |
F |
- |
- |
Smelting of ores
containing fluorine compounds will result in off-gases containing HF. Removal of HF in the gas cleaning system
depends on equilibrium conditions in the scrubbing circuit.
Addition of sodium silicate will
enhance removal of HF. |
| Iron |
Fe |
< 30
to 50 ppm |
50 ppm |
Generally the result
of corrosion of ductile iron and carbon steel piping and equipment. The amount of iron can be reduced by the use of
stainless steels as material of construction and anodic protection of carbon steel storage tanks. |
| Lead |
Pb |
< 1
to 5 ppm |
- |
Lead is present in the
smelter gases as a fume which is condensed in the cleaning
system. Proper design and operation of the
gas cleaning system will control the amount of lead reporting to the product acid |
| Mercury |
Hg |
< 1
ppm |
- |
Smelting of ores
containing mercury will result in off-gases containing mercury. Removal of mercury from the gas before entering
the contact section of the plant can be done by a number of different technologies. Due to the toxicity of mercury, reduction to
levels less than 0.1 ppm may be legislated. |
| Magnesium |
Mg |
- |
- |
- |
| Manganese |
Mn |
< 0.5
ppm |
0.2 ppm |
- |
| Nickel |
Ni |
< 1
ppm |
1.0 ppm |
Nickel can be present
in smelter off-gases or result from the corrosion of stainless steel piping and equipment. |
| Nitrate |
- |
< 5
to 10 ppm |
5 ppm |
NOx is formed in the smelter from the burning
of nitrogen containing fuels and the fixation of atmospheric nitrogen. Control of nitrate in the acid is achieved by the
segregation of candle drainings and oxidation with chemical such as hydrazine. |
| Platinum |
Pt |
None |
None |
- |
| Selenium |
Se |
< 20
ppm |
20 ppm |
Smelting of ores
containing selenium will result in off-gases containing selenium. Proper design and operation of the gas cleaning
system will control the amount of selenium reporting to the product acid. |
| Sulphur Dioixde |
SO2 |
< 50
ppm |
40 ppm |
SO2 is
dissolved in the acid when as it comes in contact with SO2 containing process
gas in the towers. Air stripping will remove
SO2 to the desired levels. Treatment
with hydrogen peroxide will oxidize SO2 to H2SO4.
|
| Zinc |
Zn |
< 1
to 40 ppm |
40 ppm |
Zinc is present in the
smelter gases as a fume and dust. Proper
design and operation of the gas cleaning system will control the amount of zinc reporting
to the product acid. |
| Organic Matter |
|
|
None |
- |
| Fixed Residue |
|
< 100
to 300 ppm |
300 ppm |
- |
| Colour |
- |
- |
- |
A ‘water
white’ acid is desireable. Coloured acid
is the result of the presence of colloidal carbon which can impart a light brown to black
colour to the acid. |
| Transmittance/Clarity |
- |
- |
- |
The presence of
suspended solids such as Fe(III) will cause the
acid to appear cloudy. |
Note 1: Federal Specification O-S-801F, Class 1, Sulfuric
Acid, Electrolytic
Federal Specification O-S-801
Federal Specification O-S-801 Revision F,
Sulfuric Acid, Electrolyte (For Storage Batteries) defines four grades of sulphuric acid:
Class |
Acid
Content (% weight) |
Specific
Gravity at 15.6ºC/15.6ºC (60ºF/60ºF) |
| Minimum |
Maximum |
Minimum |
-Maximum |
| 1 |
93.2 |
- |
1.8354 |
- |
| 2 |
49.5 |
50.5 |
1.3945 |
1.4042 |
| 3 |
36.5 |
37.5 |
1.2767 |
1.2853 |
| 4 |
28.3 |
29.5 |
1.2085 |
1.2185 |
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