39. Behind all that glitters
Department of Chemistry, Providence Women's College, Calicut 673 009
India tops the countries in the demand and consumption of gold. For an average Indian household, no auspicious event is complete without gold ornaments, finding an important place. Besides gold being used for ornamental purposes, it is a dependable and ready source of finance available to its holders.
The ornaments sold by a jeweler is understood
to be of 22 karat fineness. Invariably the consumer has to pay
the cost of 22 karat while purchasing, though its fineness is
never tested or questioned and no scientific method is employed
to determine the fineness of the gold. Trade is carried on, on
faith, though the purchaser is the loser, if it is otherwise.
The same is the case when old ornaments are sold. The jeweler
, in order to determine the fineness, resorts to the only conventional
method of rubbing the gold on a touchstone. His assessment though
arbitrary is final and thrust upon the seller, which is always
and every time advantageous to the purchaser (the jeweler). The
gold of the ornaments so collected cannot be naturally uniform
in fineness. To obtain the required fineness, the jeweler subjects
the ornaments to an elaborate acid process.
The old ornaments are melted, adding twice its weight of silver, in a graphite crucible. The molten alloy is poured into a vessel containing cold water, when thin flakes are formed. These flakes are collected and heated with plenty of concentrated HNO3 in a big stainless steel vessel. Copper (present in the melted ornaments) and silver dissolve forming the respective nitrates, leaving undissolved gold in the form of fine, brown coloured powder.
Cu + 4HNO3 Cu(NO3)2 + 2H2O + 2NO2
Ag + 2HNO3 AgNO3 + H2O + NO2
The supernatant liquid* (blue coloured due to Cu(NO3)2) is decanted. The brown powder which looks like mud is collected and melted in a graphite crucible when glittering pure yellow metal is obtained. During this process, huge volumes of nitrogen dioxide (NO2) escape into the atmosphere, NO2 is an acidic oxide which is known to cause acid rain, photochemical smog; and asthma and other respiratory disorders.
On inhalation, NO2 combining with oxygen and moisture forms globules of HNO3 in lungs, as could be seen from the following equation.
4NO2 + O2
+ 2H2O 4 HNO3
Lung comprising thin membranous tissue would be greatly affected by the acid thus formed.
NO2 being acidic in nature can get easily absorbed in slaked lime[Ca(OH)2], forming Ca(NO3)2, which is a good fertilizer.
2Ca(OH)2 + 4NO2
+ O2 2Ca(NO3)2
For this purpose a suitable vessel packed with the absorbent, Ca(OH)2 and coconut fiber,
in alternate layers has been designed, and found to be effective in absorbing NO2.
The supernatant liquid*, decanted in the previous process contains silver in the form of AgNO3. To recover silver, the above solution is diluted 15 - 20 times with water. Into the diluted solution thick copper rods are immersed. Due to displacement reaction, silver gets deposited on the copper rod in the form of powder.
2AgNO3 + Cu
Cu(NO3)2 + 2Ag.
After recovering silver the remaining solution contains plenty of nitric acid and copper in the form of Cu(NO3)2. This solution is discarded without any treatment. As a consequence, there is the risk of soil and the nearby water bodies being contaminated with HNO3 and Cu(NO3)2. In acidic soil, microbial population can get reduced/altered. Earthworms are not capable of surviving below pH 4.5. Therefore the soil may become unfit for cultivation.
1) The decanted liquid can be subjected to distillation and HNO3 can be collected and recycled.
2) The residual content of the distillation flask can be diluted with water. To this solution, calculated quantity(depending upon the quantity of the silver to be recovered) of Na2CO3 can be added, when Ag2CO3 (yellow precipitate) gets precipitated. The precipitate is allowed to settle and collected by decanting the supernatant**
4Ag + 2CO2 + O2
The above** supernatant solution is further treated with Na2CO3 when copper precipitates as CuCO3.
Cu(NO3)2 + Na2CO3 CuCO3 + 2NaNO3
From the precipitated CuCO3, copper can be recovered and recycled. The remaining solution can be allowed to evaporate using solar energy(the cheapest available energy) and NaNO3 can be recovered which is yet another useful fertilizer.
The polishing of the ornaments is done by electrolysis. Potassium cyanide or sodium cyanide is used in the electrolytic bath, along with some plant resins, sealing wax. The contents of the electrolytic bath, after repeated use is discarded- again without any treatment to nullify the toxic effect of cyanide.
To summarize, since only traditional artisans are working in this field, proper education regarding the chemicals they use, and the formidable consequences of the process is the first and foremost need. Jewelry production does not seem to be considered as an industry and hence there is no restraint on the quantity or the variety of toxic chemicals used in the purification, soldering and polishing processes. No pollution control measures are employed, nay not even be contemplated, and they are at present happily indulging in the process with impunity. If scientific methods are introduced for proper management of the effluents/process, a welcome step in the direction of pollution control would have been taken. The people engaged in the process are in blissful ignorance of the alarming situation and therefore the situation cries for immediate scientific intervention.
What is iodized salt?
Common salt (which is mainly sodium chloride)
is obtained by evaporating sea water in salt pans, using solar
energy. For this reason, it is called solar salt. On further
purification, the sample obtained is devoid of the contaminants
which are the salts of calcium and magnesium. The removal of
these salts makes the salt dry and is free flowing in nature.
To this dry sample of sodium chloride, potassium iodide or potassium
iodate is added up to a concentration of 20ppm. Hence the iodized
salt is sodium chloride from which calcium and magnesium salts
have been removed by purification and to which KI or KIO3
The chemistry of iodine and iodide
Iodine is one of the members of halogen family. It is the most beautiful of all the elements (2). It is a black shining crystalline substance. It's solution either in water or any other organic solvent is brown in colour. It's vapours are violet in colour. Iodine is subliminal in nature. Of all the halides the size of iodide ion is the biggest. For this reason iodides are most soluble in water. It is a very strong reducing agent. It easily gets converted to iodine, when exposed atmospheric oxygen, especially in acid medium (3).
2 I I2 + 2e
(Iodide is represented as I and
Iodine as I2 and e in the above equation is electron)
The importance of calcium and magnesium
These two metal ions are very essential nutrients. They have vital roles to play in body functions. Magnesium is required for a number of enzymatic reactions, connected with energy transactions in the body. Magnesium is a cofactor of many enzymes and is contained in metalloenzymes (4). The construction of biomolecules requires energy in the form of ATP and whenever there is ATP, there is an obligatory need for magnesium (5). Magnesium ions inhibit the growth of calcium oxalate crystal in vitro and there are reports that renal stone development in vivo is inhibited by prolonged administration of MgO (6). Evidences have been reviewed recently, suggesting and inverse relationship of magnesium in drinking water to cerebrovascular and cardiovascular diseases (7). An inverse relationship between the incidence of strokes and the hardness of drinking water has been reported (8). Calcium is essential to maintain healthy bones and teeth. It is required to trigger the contraction of the muscles to maintain the regular beating of heart (9). Calcium is essential for neurotransmitter release, as well as for the release of hormones (10).
It was the year 1900, an American doctor
David Marine suggested that iodine (in the form of iodide) be
added to drinking water and TABLE SALT (11). Small amounts of
iodine are required in our diet. So, traces of sodium iodide
are added to TABLE SALT (12). The new Encyclopedia Britannia
(13), defines iodized salt as TABLE SALT with small amounts of
iodine added, usually as potassium iodide to guard against the
dietary deficiency of iodine. The new book of knowledge says
salt sold for table use often has iodine added to it to prevent
disease called goiter (14). The word TABLE SALT has to be taken
note of, in all the above cases. Table salt is, what is used
on dining table without being subjected to cooking. In our Indian
context the word table salt has become synonymous with powder
salt. Further we don't differentiate table salt from cooking
The two unintended disadvantages to iodized
salt are: (i) Calcium and magnesium get eliminated while the common
salt is purified; (ii) The iodide that is added to the salt escapes
as iodine while cooking/storing. As a result the very purpose
of switching on to iodized salt is totally defeated and the loss
in nutritional value is manifold.
The remarkable successful method is the
injection of iodized oil, from which iodine is slowly released,
the effect of a single injection lasting 3 to 5 years. Pioneered
in New Guinea, this method has now being applied with striking
benefit, in other parts of the world (15).
The following remedial actions are suggested:
1. The ban on the sale of unionized salt should be lifted with immediate effect in all the states of the country.
2. The use of common salt (solar salt) should be encouraged deployed on a large scale at state level.
3. Other means of supplementing iodine, such as iodized oil should be thought of and
4. The nation wide myth of iodized salt being beneficial is to be exploded, with appropriate education at all levels.
1. Jan, Nutrition, National Institute of Nutrition, Hyderabad (1989).
2. Discovery of elements, Paico Publishing House, Cochin (1967).
3. Therald Moeller, Inorganic Chemistry An Advance Text Book, Asia Publishing House 5th edition, (1956).
4. F.W. Oehme, ed., Toxicity of Heavy Metals in the Environment, part -2, Marcel Dekkar, Inc. New York and Basel, (1979).
5. J. K. Aikawa Magnesium; Its Biologic significance CRC press, Inc. (1981).
6. D. J Weatherall, J.G.G. Ledingham, D.A. Warrel, ed., Oxford Text Book of Medicing, Vol -2, Page 18. 92, ELBS, Oxford University Press. (1988)
7. Takahashi . E, Geographic Distribution of Mortality rates from cerebrovascular diseases in European countries, Tohoku, J. Exp. Med, 92, 345, (1967).
8. Kobayashi. J., On Geographical Relationship Between the Chemical Nature of River Water and Death rates from apoplexy. Ber, Ohara Inst. Landwirtsch, Biol.Okayama Univ., 11,12., (1957).
9. J.D. Lee, Concise Inorganic Chemistry, p-353; IV.
10. As in Ref (6) - p-10.51.
11. Molecules to Man, published by American Institute of Biological Sciences P-536., (1963).
12. As in Ref -(9)- p-590.
13. The New Encyclopedia Britanica, 15th Edit. Vol-6.
14. The New Book of Knowledge, Grolier Incroporated, Dangber, Connecticut, Vol - 17, p-21.
15. As in Ref (6) - P-10-36.
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