GENERAL INFORMATION

The Mirovsko rock-salt field is located at five kilometers South-Eastern from town of Provadiya. It is unique as per its conditions of occurrence, form and chemical composition. It has the shape of a truncated cone, as the shallowest part occurs at depth of 15-20 meters, and its depth reaches up to 3600 meters. The salt-rock mass, out of which the field is formed, contains average 69,6% NaCl and 23,3% insoluble admixtures, given by marls and clay schists, anhydride and etc. The Mirovsko salt field is the only one exploited in the country and Provadsol EAD takes special care and investments to guarantee its long-term exploitation.

History

The extraction of salt in the region has already existed at the time of the Neolith (7000 years ago). Then the ancient people boiled the salt water from the local springs and so they obtained the precious product.
The modern history of the Mirovsko salt field began from 1917, when it was accidently discovered by Stoyan Sabev.
The first drilling researches of the rock-salt field were made by the mining department of the Ministry of Commerce from 1926 until 1928. The first geologic-exploration drilling, which proved salt from a drill core, was cut in 1926 by engineer Georgi Konstantinov from the city of Varna .
The extraction of salt from the over-stock mineralized waters exists from 1924 until 1960. The extraction of salt through underground (mining) method began in 1954 and continued until 1964.
The exploitation through drillings begins in 1954 and continues today. It began with the building of the first soda factory in Bulgaria. It is exploited through drillings with underground dissolving of the rock salt. There are three horizons developed - 1000, 1250 and 1750 meters at conditional network of location of the drillings 200 х 200 meters. In the salt-rock mass chambers are formed (cavities, filled with brine) with diameter of 100 meters and a height from 100 up to 400 meters. The exploitation is led from the bottom upwards at stages from 10 up to 70 meters. There are 40 drillings, with which annually up to 4 million tons of salt may be extracted.
On 03 August 2000 the former enterprise Geosol became property of Solvay Sodi, as it was renamed to Provadsol. The next important step was done on 28 August 2000, when with the Ministry of Economics was concluded a contract for giving of concession for output of rock salt for term of 30 years.

Process

For the production of brine is necessary the washing away of the drillings to be led at a permanent regime, as it is stopped only at their repairing (shortening, trouble with the working columns, control tubules or equipment and etc.) 
The water enters in 35 000 м3 equalizer from the derivation artificial lake Tsonevo in workshop Razsoldobiv. From there it goes in a water-receiving well, and then through pumps it is sent in a reservoir for water. From where, through multi-step rotary pumps it is passed in the drillings. In the chamber of the drilling the water dissolves the rock salt and gets out salted. This process is permanent. The slight brine produced from the drillings and the waste water, are collected in a reservoir for slight brine. From it they are sent for additional saturation in specified for this drillings. The produced saturated brine enters in a reservoir for finished brine. From it through rotary pumps it is passed at brine-pipeline for Solvay Sodi.

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