Jökull - 01.12.1961, Blaðsíða 64

and calcium carbonate in pores and fissures
near to the surface suppresses the flow and
may in some cases completely close all surface
outlets.The implications will be discussed below.
The geothermal fluid is also capable of a sel-
ective transport of a great number of other
components. Many geologists are of the opinion
that a number of metalliferous deposits are for-
mecl by geothermal activity.
The relevant problems are treated at length
in three important papers by White (1955,
1957a, 1957b). Examples are pressented of the
connection between thermal activity and de-
posits of quicksilver, antimony, manganese,
tungsten, gold, silver, fluorite, sulphur and
arsen. White presents also a thorough discussion
of the geochemistry of thermal waters.
But the recovery of chemicals from active
thermal areas is at present of minor economic
importance. The chemical industry in Tuscany,
Italy, is, in fact, the only producer of chemical
components from geothermal fluids. Some int-
eresting studies have also been made in New
Zealancl.
(b) The chemical industry of the Larderello s. a.
The various aspect of the recovery of chemi-
cals in connection with the large power pro-
duction of the Larderello s. a., Tuscany, Italy,
are discussed at considerable length by Garbato
(G/63) and Lenzi (G/39). A part of their treat-
ment is devoted to the removal of corrosive
gases and impurities from the steam in the
power-cycle. These aspects are beyond the scope
of the present report.
The activities at Larderello started in 1827
and were at that time solely devoted to the
recovery of boric acid from the thermal springs.
The power generation was initiated at the be-
ginning ol' this century. As of now the power
generation is by far the main industry and the
recovery of chemicals from the thermal fluids is
only a relatively small business. The main chemi-
cals are boric acid, carbon dioxide, sulphur,
ammonium sulphate and ammonium carbonate.
(i) Boric acid. The natural-steam at Larderello
contains about 200 parts per million by weight
of boric acid. The primary step in the recovery
of this component consists in the washing of the
steam by water. Water is purnped into the steam
pipes from the wells ancl separated out again.
The solution obtained contains about 3.000
ppm of boric acid. The solution obtained con-
centrated by evaporation and the boric acid
recoverecl by crystallization.
The washing of the steam leads to the loss
of its superheat and implies a loss in power pro-
duction of about 4%.
(ii) Carbon dioxide. The natural- steam con-
tains about 4% by weight of carbon dioxide.
There are therefore at hand very large quanti-
ties of this gas. A plant for the production of
liquid and solid carbon dioxide was erected in
the late thirties but this procluction came to an
end at the beginning of the war.
(iii) Sulphur. The large amount of hydrogen
sulphide in the natural-steam at Larderello,
about 80 ppm, presents problems because of air
contamination. There are therefore installations
for the removal of this gas. The removal is ef-
fected either by an absorption by means of an
iron-oxide becl or by an absorption into an
alkaline arsenic-solution. The oxidization of the
gas gives elemental sulphur which is procluced
is bars.
(iv) Ammonium sulphale and ammonium car-
bonate. The natural-steam contains about 200
ppm of ammonia. This gas is recovered from
the steam-transformers of the indirect power-
cycle applied in the older power plants. It is
converted into the sulphate and carbonate.
This industry is of minor importance.
(c) Experimental production of lithium and
other materials jrom thermal water
in New Zealand.
Kennedy (G/45) presents a discussion of the
possible recovery of chemicals from the thermal
waters at Wairakei in New Zealancl. As of now
the thermal water issued by the wells transports
a total of 105.000 tons/year of sodium chloride,
13.000 tons/year of potassium chloride ancl
2.400 tons/year of lithium carbonate. The esti-
mated value of these chemicals is about 6 shil-
lings per 1.000 gallons of water.
The chemicals can be recoverecl by a combi-
ned electrodialysis-evaporation procedure. How-
ever, the total cost of recovery amounts to 7 or
8 shillings pr. 1.000 gallons of water. The
process is therefore not economical. A compre-
hensive discussion of the problems involved is
presented and experiments are describecl that
have been carried out in order to study the
relevant problems.
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