Paliorema Sulfur Mine and Processing Plant, Milos

Introduction

The ruins of Paliorema Sulfur Mine on the Greek island of Milos are remnants of an important period of industrial history on the island. Milos contains abundant mineral deposits of volcanic origin including sulfur, manganese, bentonite and perlite, all of which were, or continue to be, subject to industrial exploitation. Mining of Sulfur has long ceased to be economical in developed countries since abundant supplies are available as by-products of refining of sulfur-rich hydrocarbons. Pure sulfur is still extracted on a small scale at several volcanic sites such as Kawah Ijen in Indonesia, although this relies on low labour costs and the absence of the need for extraction processes from ores.

In its final years of operation, the sulfur processing plant employed the innovative Svoronos method for highly efficient recovery of sulfur from ore. This method was employed by the Milos Sulphur Mines S.A. from 1952 to 1958 until it went bankrupt following a massive drop in sulfur prices. Today the buildings are in a rather desolate state with most roofs missing, thus exposing the machinery, which largely remained in place, to the elements. Many smaller items have been removed, some to the local mining museum, whilst many others have been stolen as access to the site is not restricted.

Ruins of Svoronos process sulfur-processing plant	Sulfur-processing plant viewed from beach	Paliorema Bay with mine buildings

Mine Layout

Maps are available showing the layout of the mine (Milos Sulphur Mines, Gregores Belivanakes, ISBN 960-91562-2-3; Annexes). The main sulfur bodies from which ore was extracted were located underground and accessed by horizontally driven tunnels (adits). The mine adits contained narrow-gauge rails on which minecarts were moved by hand. The rails further connected the mine adits to the main processing facilities and also to the dock facilities for loading the sulfur onto boats. One adit entered south of the administration buildings and connected to possibly the first major underground deposit mined in the valley, since an early ore mill was constructed at its exit. The main bodies of sulphur mined in the final years of operation were however located in the hillsides flanking the valley several hundred meters west of the main mine buildings and were linked to the processing plant area by the main No.1 (or "Ace") adit. The rails connecting processing plant and dock crossed a small stone bridge as they progressed towards the dock which had a crane for lifting ore onto waiting ships. A further bridge connected the auxiliary buildings to the processing facility at the height of the construction bureau.

Todays mine layout largely derives from a period of construction starting in the late 1930s, when a major modernization program was implemented, including the construction of the main hill-side sulfur processing plant which forms the most prominent part of the ruins today. Further auxiliary buildings housing offices, accommodation, laboratories, workshops and the generator were constructed during this period. The plant has a twin-railed sloped incline for transporting ore from a storage bunker at its base to the top of the processing facility. From here the ore was passed through the processing facility and was crushed before sulfur was extracted by heating followed by separation by sieving and flotation processes, as shall be explained in more detail in the following section.

Paliorema valley with mine and processing facilities	Main processing plant	Remains of dock facility

View from valley with track of powered incline in front of processing buildings	Manpower-operated tippable minecart for ore transport from mine to processing facilities and from the latter to the dock

Sulfur Processing Plant (Svoronos Method)

At Paliorema, sulfur ore was not only mined but also processed before relatively pure sulfur was shipped from the site. Initially, sulfur was extracted from crushed ore by heating the latter in a set of kilns. In the kiln, the sulfur was melted and a proportion of it would manage to flow to the bottom of the kiln where it could be collected. Various forms of this process were used at Paliorema, progressing from the Calcarone process to the Doppioni, and finally Gatto-Gill process (although the 1957 Krupp Report suggests that the Calcarone process was still being used in 1939). The Calcarone process generally involves a large kiln with a sloping base with a grid at the lower side. After igniting the sulphur, the top of the kiln was covered with slag, thus reducing access of oxygen and reducing combustion. As the sulfur burns, a proportion melts and drains to the bottom of the kiln. Pollution is significant, yet reduced to some extent compared to the most basic open-topped oven types (Calcarella (probably not used at Paliorema)) but the process takes 1-3 months (depending on size). Combustion of significant amounts of the sulfur is a further disadvantage of the process.

The Doppioni process involves the use of two connected chambers. One vessel is generally heated using e.g. wood or coke and this causes melting and finally (above 410'C) evaporation of sulfur. The sulfur gas passes through a pipe into the second chamber in which it cools and condenses, allowing it to be collected in relatively pure form. The basic principle of cooling sulfurous gases to achieve condensation can be seen in a simple form today at Kawah Ijen sulfur mine, where fumarolic gases are cooled in pipes with liquid sulphur being collected at the bottom of them.

In the Gatto-Gill process, a series of chambers is used with the exhaust gases flowing to adjacent chambers which are thereby preheated and finally catch fire. The process is similar to the Calcarone process insofar as sulfur is collected at the base of the kiln, which again has a sloping base. The kilns are however smaller and the process can run continuously if an array of kilns is used.

Even with the most advanced Gatto-Gill process, recovery of only about 35% of the sulfur within the ore at Paliorema could be achieved, compared to 65% in sicilian deposits using the same method (Ekonomopoulos, 1952, Ind. Engineer. Chem. 44(1), p.105-106). This was a result of the properties of the locally mined tuffaceous ore which tends break down in the smelters once the sulfur is fluidized and thus obstructs passage of sulfur to the base of the kiln. Further, the process also results in the release of noxious sulfurous gases, particularly sulfur dioxide. These had a debilitating effect on the early miners at Paliorema with many dying of lung conditions, in particular consumption (pulmonary tuberculosis).

The processing plant which lies in ruins today was constructed in the late 1930s and briefly used in 1940 before disruption by the war. Operations resumed in 1953 and the plant continued to operate until 1958, producing about 15000 Tonnes of Sulfur in this period. The plant was constructed for processing sulfur-containing ore by the Svoronos process.

In 1927, the greek inventor Jason J. Svoronos applied for a greek national patent (GR1560) for a novel form of sulfur extraction from ore. An equivalent patent was applied for in germany in 1937 (DE703159). The process no longer relies on combustion of sulfur and yields as much as 90% of the sulfur entrapped in ores. In the process, the sulfur-containing ore is crushed and then basically heated in a solution at a temperature of about 120'C. The sulphur melts at this temperature and upon cooling, small lumps of sulphur form which can be separated by a flotation process. Looking at the mine layout at Paliorema (based on technical diagram of Hungarian Stefka, drafted in 1966 (Annex 6 in "Milos Sulfur Mines")), it is however evident that 2 heating steps were employed, at least at some stage during the facilities operation. This is in line with the teachings of a slightly more recent patent by Svoronos (DE864232, patented 27.07.1938; Based on greek patent applications filed on 26.07.1937 and 22.01.1938).

DE864232 explains the process in some detail. In a first step, the ore is ground to the size of a hazelnut and then loaded into a pressure cooker, in which it is heated to a temperature of at least 120'C for a time sufficient to melt the sulfur in the ore (the cooker may alternatively contain a solution that doesn't boil until at above 120'C at atmospheric pressure, in which case the vessel would not need to be pressurized). During heating, the mixture is agitated to further break up the ore and to allow the molten sulfur to start to form small globules (granule size can be influenced by speed of agitation). The mixture is then allowed to cool, whilst agitation continues. This ensures that the sulfur globules remain small and solidify to granules with a diammeter of less than 1 mm. The material is sieved to remove any rock fragments over 1 mm in size. At the end of this first step, one thus obtains a mixture of sulfur granules and small fragments of the tuffaceous rock in which the sulfur was embedded.

In the second step, the sulfur must be removed from the fine rock fragments. The mixture from step 1 is again heated in a pressure cooker to melt the sulfur, this time with gentle or no agitation. In the presence of higher sulfur concentrations and without significant agitation, molten sulfur forms larger globules. After cooling, one obtains a mixture wherein the rock fragments remain at or below the cut-off size of the sieving process at the end of stage 1 (e.g. less than 1 mm), whilst the sulfur granules are now significantly larger. A further sieving step can now be employed, wherein the sulfur is retained by the sieve and the small rock fragments pass through it and are thus removed. Alternatively to step 2, a flotation-separation process is suggested (as in the earlier patent).

The process actually employed in the processing plant at Paliorema is based on the above patent, yet based on documents from the German Krupp company, which visited the mine shortly before its closure and documented the process, some modifications appear to have been in place. The text of the report suggests that a single pressure cooker was used and no flotation step was employed. A purifying autoclave in a building adjoining the plant was then used. This is under further investigation. The plan of the plant (according to Stefka) and a greek translation of the text of the Krupp Report are found in the book "Milos Sulphur Mines" (ISBN 960-91562-2-3). It is certainly puzzling that the upper silo appears to have been converted to accommodation - there is no connection from elevator to silo and several bedframes are found in the chamber that houses the silo according to the plan of the plant.

The processing equipment was spacially arranged in the plant as follows (based on Stefka Annex). After being transported up the incline, the ore passed through a sorting and crushing process in the rooms nearest the incline, was then elevated to the top of the middle row of rooms in which it was heated to extract sulfur and again subjected to size-sorting processes, following which it was lifted by conveyor belt to a silo above the final set of rooms containing a second heating apparatus for further separation of sulphur from the rock followed by size-sorting / flotation-separation to isolate the sulphur. Further buildings located on the valley floor below the main plant were presumably for storage or further refining steps. The two Gilardoni centrifugal hammer-mills were for powdering the product before packaging for shipping and were only installed shortly before closure of the plant. In particular, on the diagram of the plant (Stefka) it appears that whilst two sequential heating steps are employed, each followed by sieving steps, the second sieving step is followed by a flotation step (i.e. the two alternatives for step 2 in the DE864232 patent appear to have been combined to achieve improved purification).

Sulfur kilns used prior to construction of Svoronos Plant	Sulfur crystals embedded in tuffaceous material (sulphur ore), Paliorema. (Average Sulfur content is about 15-20%)	Sulfur kilns used prior to construction of Svoronos Plant

Remains of winch of smaller incline linking lower rails with rails at storage bunker level.	Remains of storage bunker at base of main powered incline	View up twin-tracks of main powered incline. Used to move ore from bunker to processing facility.

Large funnel for capturing ores tipped out of wagons at top of sloped incline	Swinging transport band and vibration sieve for first separation of ore by size prior to crushing step 1	Elevator for transporting crushed ore to silo above first rotating boiler

Top of elevator	Former silo at top of elevator. Rusting bedframes suggest it was eventually put to alternative use

Bunker for storing material after processing in rotating boiler	"Mixer" (exact function unknown) at base of conveyor belt taking material to silo above second heating apparatus (the autoclave)	Conveyor belt taking material to silo of autoclave. Part of chimney lies on track

Top of conveyor belt taking material to silo of autoclave	Rails leading from silo at top of conveyor belt (Function unknown)

Main boiler room. Used for generating heat for processing boiler and autoclave. Boiler is encased in brick wall bottom right.	Remaining bottom section of chimney	Oil-burner powering main boiler

Core part of Svoronos processing plant: autoclave and sieving machinery	Opening of storage silo above autoclave	Rotating autoclave driven by 10 hp motor. Top right is funnel for loading autoclave (and measuring load).

Storage bunker above sieving / flotation machinery	Sieving / flotation machinery for separation of sulfur from remaining rock fragments	Base of sieving / flotation machinery

Refining autoclave in building adjacent to main processing plant complex.	Unknown sulfur refining machinery at base of hillside processing plant.	Gilardoni centrifugal hammer-mills (For breaking sulfur clumps into powder form)

Storage tanks in processing building at base of hillside processing plant	Gilardoni centrifugal hammer-mill	Mine with bridge and small constructors bureau in foreground

View from above processing plant. Dock facility at top left corner of image.	Stone bridge with rails for transporting sulfur from processing plant to dock facility. In the final years of operation ore was transported by lorry to Adamas port.	Remains of dock facility. Crane has fallen into water.

Generator Shed, Workshops, Laboratory & Administration

On the southern side of the Paliorema valley are several auxiliary buildings. Nearest the sea is the largest concrete building, the combined office / accommodation block. Moving inland one sees a number of buildings for storage, housing the main diesel generator and machine workshop, and further blacksmith and carpentry facilities. Furthest inland is a workers accommodation block.

View over auxiliary buildings from top of powered incline of processing plant.	Workers accommodation block

Main diesel generator for mine	Mobile generator / compressor (?) for driving mine machinery	Maintenace building

Abandoned workshop	Abandoned workshop

Accommodation & Office Block

	Accommodation / Office Building

	Inside first floor of accommodation

Underground

The hillsides containing the sulphur deposits contain a large number of horizontal tunnels (adits) accessing the actual underground deposits. The main adit in the Paliorema valley was No.1 ("Ace") adit. This connected the main sulfur bodies to the processing plant. Following a landslide the remains of the entrance and adjacent storehouse have now been buried. Mining was initially performed using simple tools but later pneumatic drills were employed. The use of explosives was also common and these were stored away from the main mine buildings for safety reasons.

Several further tunnels can be found in the vicinity of the dock facilities. The function of a short tunnel under the rails to the dock in unclear. A longer tunnel (No. 0) adjacent to the location of the crane may have been used for storing empty minecarts during ship-loading.

Conditions underground were harsh. Due to residual hydrothermal activity and exothermic reactions occuring as the sulfur-bearing ore was exposed during mine operations, temperatures of over 40'C were reached in certain parts of the mine. Sulfur dust mobilized during drilling operations also severely affected the lungs of workers. Following a number of court cases brought by miners, the company worked on improving ventilation in the mine during its latter years of operation. Mine adit No.2 was constructed for ventilation purposes and had a large fan installed at its entrance. Several further ventilators were in use and compressed air was also pumped into the mine for ventilation purposes, in addition to driving the pneumatic drills.

	Tunnel No. 0 by dock facility

Entrance to horizontal mine-shaft (adit) No. 2. This shaft was used for ventilation in the final years of operation. The circular concrete entrance housed a large fan,	Short tunnel near dock. Roof is supported due to rails passing overhead

Gas-mask for protection against sulfurous gases, Milos Mining Museum	Ventilator for use in mine, Milos Mining Museum	Mining tools, Milos Mining Museum. Small pneumatic drill is visible.

Additional Features

	Support for piping through which seawater was pumped to water reservoir above sulfur-processing plant

Visitor Information

Paliorema mine can be reached by car via a rough unpaved road. Signs in greek to the "Sulfur Mine" should be followed. Only 4WD vehicles should attempt the last stretch of road. Other vehicles can park at the quarry before the road enters the valley or in the corner above the mine (although limited space is available).

The mine buildings are unstable, including the concrete floors which appear to be made of thin and poorly reenforced concrete. Hence, entry to buildings is unsafe, also as parts of heavy machinery, roof elements etc. may collapse at any time. Mine entrances are not all sealed off, but entering these is dangerous since the tunnels may not be stable and the air quality in the mine may be dangerous. Visitors are asked not to remove any industrial relics from the mining buildings. Indeed it is to be hoped that plans to preserve the site can be implemented before it decays beyond repair.

Visitors should combine a visit to Paliorema with a visit to the Milos Mining Museum near the southern exit of Adamas town. The museum has been kindly sponsored by S&B Mining Corporation, who presently run much of the mining activities on the island.

Milos also has a number of other geological sites of interest. See main Milos page.

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