Recovery of Potassium Fertiliser Salts from Sea Bittern

Code No: TMS163 Price: Rs2400/- Category: Environment: Recovery


Summary  : Potash is an important plant nutrient. Worldwide, over 90% of Potash consumption is for Fertliser application. Indian Potash consumption has grown steadily over years at an average growth rate of 9.5%. India imports its entire Potash requirement, which amounted to approximately 1557000 tonne in 2000-2002. There are no viable land based Potash reserves in India but it has Seawater, which is a possible source of Potassium salts though of low concentration. During extraction of Salt from Seawater by evaporation, Potassium salts get concentrated in Bittern, an effluent of Salt Industry. Indian Salt industry produced 14.45 million tonne of salt in 1999, despite loss of production in Gujarat due to severe cyclone. Bittern generated in Salt industry contains Potassium fertiliser salts in addition to other important chemicals. Potential of recovery of chemicals from bittern in India has not been fully exploited. Considering significance of developing indigenous source of supply for Potash, which is important both for the Agricultural and strategic reasons, a Techno-Market Study has been carried out.

Year of Publication : 2002

Table Of Contents : Chapter 1 - INTRODUCTION: Potash Fertiliser Consumption in India; Potash Imports; Indian Salt Industry; Bittern-Potential Source of Potash; Scope of Study & Methodology; Chapter 2 - MARKET SCENARIO: International Supply, International Demand, Potash Market in India; Chapter 3 - TECHNOLOGIES FOR POTASH RECOVERY IN OTHER COUNTRIES: J.H Hidebrand Process, Dead Sea Works Ltd., Israel, Arab Potash Company, Jordan, Bonne Ville Solar Evaporation Process, Searles Lake, USA, Great Salt Lake Minerals & Chemicals Corpn., USA, Potash Recovery at Salar de Atacama, Chile, Potassium Sulphate Recovery from Da Chaidan Salt Lake Brine, China, France, Greece, Italy; CHAPTER 4 - TECHNOLOGIES FOR POTASH RECOVERY IN INDIA: Work at Central Salt & Marine Chemical Research Institute, Work at Regional Research Laboratory, Bhubneshwar; CHAPTER 5 - PROSPECTS OF POTASH RECOVERY FROM BITTERN IN INDIA: Market Acceptance, Feasibility Analysis, Availability of Raw Material - Bittern, Utilisation of Surplus Land with existing Salt Units, Ambient Temperature and Evaporation Rate; CHAPTER 6 - IDENTIFICATION OF TECHNOLOGY: Technology Evaluation, Constraints for Potash Recovery from Bittern in India, Future Course of Action; CHAPTER 7 - RECOMMENDATIONS, IMPLEMENTATION & ACTION PLAN: Recommendations, Implementation & Action Plan, Expected Benefits, Spin Off Benefits. ANNEXURE 1: Summary of Primary Survey; ANNEXURE 2: Specification for Potassium Chloride, Fertliser Grade; IS 2779-1980; ANNEXURE 3: Specification for Potassium Schoenite; IS 6661-1972; ANNEXURE 4: Specification for Potassium Sulphate, Fertiliser Grade; IS2764-1980; ANNEXURE 5: Result of Patent Search; ANNEXURE-A: List of Salt Units producing more than 50,000 TPA; ANNEXURE-B: List of Interested Organisations; ANNEXURE C: Minimum & Maximum Temperature in Salt Producing regions; REFERENCES; GLOSSARY; KEYWORDS; FIGURES

1 .Potash is an essential plant nutrient. 90% of Potash is consumed as fertiliser. It is also basic material for other industrially useful chemicals like Potassium chlorate, nitrate, sulphate, hydroxide, carbonate etc.

2. India's Potash consumption in 2000-2001 was 1.55 million tonne. With no significant land based source of Potash, it imports it's entire requirement of Potash. Foreign exchange outgo on this account amounted to 340 million US Dollars in 2000-2001.

3. Seawater along the 5600 km. long coastline of India is a potential though dilute source of Potash. More than 70% of salt produced in India is from seawater. Indian Salt industry produced 14.45 million tonne of Salt in 1999. Gujarat,Tamiinadu and Rajasthan account for 96 % of country's salt production. Gujarat is the leader with 69% share.

4. During manufacture of Salt from seawater, inland brine or sub-sqii brine, Potassium Chloride gets concentrated to 2.5 g/ 100 mi. of mother liquor called bittern. Presently Potash is not extracted from bittern in the country though it constitutes a potential reserve of 350,000 tonne of potassium chloride.

5. This Techno-Market survey on Recovery of Potassium Fertiliser salts from bittern has the following terms of reference:

  1. Relationship and the importance of the specific topic to the broad area to which it belongs (in brief).
  2. The status of the technology in the world. Industries abroad where Potassium salts are being recovered successfully from sea bittern indicating the technological routes for production, processes, steps etc.
  3. Market (domestic/ export) sizes and their potentials.
  4. Status of technologies available in India along with the centres of development.
  5. Assessment of the technology, resource parameters such as energy, raw material, infrastructure and manpower etc. to arrive at preferred technology options available to the country. Patent for the concerned technology in India & abroad.
  6. Highlighting the deficiencies in our technology along with the cost estimates for its development & up-gradation. Reasons as to why Indian efforts at commercialisation have failed so far - Constraints and barriers for technology adoption.
  7. Highlighting ideal centres for up-gradation. (industry as well as R & D)
  8. Short term & long-term economic aspects of preferred options along with their feasibility.
  9. Impact of the preferred option(s) by itself and its spin off.

6. World production of Potassium Chloride in 1998 was 41.4 million tonne averaging a growth rate of 3.2% p.a. in last five years. Major producer is Canada followed by CIS countries. World consumption of Potash has touched 40.1 million tonne in 1998 growing at an average rate of 4.27% p.a. in last five years. Asian continent with 28% share account for highest consumption along with North America. Within Asia, China and India are the major consumers.

7. India's demand for Potash is primarily for Fertiliser manufacturing and has grown at 8.45% to 1.4 million tonne in 1999. More than 50 % of India's import of Potash is from Jordan and Israel, where it is recovered from Dead Sea brine. High concentration of salts in Dead Sea brine can be compared to bittern as a source of Potash.

8. Dead Sea Works Ltd., Israel extracts 2.7 million tonne per annum of Potash from Dead Sea brine at its plant at Sodom. It uses solar evaporation saving large amount of fuel to evaporate brine yielding salt and then Carnallite. Impure Carnallite, crystallised in solar ponds is harvested by dredgers and pumped to beneficiation plant. Carnallite is decomposed with water dissolving Magnesium Chloride and leaving mixture of Potassium and sodium chloride. Potassium chloride is extracted by thermal dissolution and crystallisation process.

9. Arab Potash Company, Jordan produces 1.8 million tonne of Potash from Dead Sea brine at its plant North of Aqaba. Brine is pumped to solar evaporation ponds, where at first salt is precipitated and later Carnallite is crystallised. Impure Carnallite is leached with water to dissolve Magnesium Chloride. Hot crystallisation technique is used to separate Potassium Chloride from Sodium Chloride. Potash so recovered is dried, ground and screened before packaging.

10. Dead Sea Works Ltd. and Arab Potash Ltd. have been using Cold Crystallisation technique for Potassium extraction from Carnallite, which technique consumes less energy.

11. At Bonneville, bittern is evaporated to separate Potassium Chloride. Impure Potassium Chloride is processed further by flotation using amine-oil collector to isolate Potassium Chloride.

12. Searies Lake, brine has high concentration of Potassium Chloride. Brine from upper zone is,concentrated in triple effect evaporators; where sodium chloride & Burkeite precipitates leaving liquor rich in Potash & Borax. Potassium Chloride is crystallised in three stage vacuum coolers.

13. Great Salt Lake Minerals & Chemicals Corpn. processes brine from Great Salt Lake for Potassium Sulphate, Salt and Sodium Sulphate. Lake brine is evaporated in ponds. In initial group of ponds, salt precipitates while in last group of "harvest" ponds, main product is mixture of Potassium salts - Kainite & Carnallite, from which Potassium Sulphate is produced. Potash is recovered as Schoenite, Carnallite and Kainite. All products are converted to Schoenite before lixiviation with hot water. Schoenite is separated & treated with fresh water in crystailiser. Magnesium & some of the potash dissolves leaving Potassium Sulphate. Sodium Sulphate is also recovered as by-product.

14. Similarly, Potash is also recovered at Salar De Atacama, Chile and at Da Chaidan lake, China. Potash recovery from brine has also been reported from France, Greece and Italy.

15. In India, Potash is not recovered commercially from bittern at present. Central Salt & Marine Chemicals Research Institute (CSMCRI), Bhavnagar and Regional Research Laboratory, Bhubneshwar (RRL) have developed techniques for recovery of Potassium salts for Fertiliser use.

16. Mixed Salt is the basic raw material for production of Potassium Schoenite or Potassium Chloride and Sodium Sulphate. Mixed salt is obtained by solar evaporation of 29.5o Be' bittern. The mother liquor after evaporation contains Magnesium Chloride, Potassium and Sodium Chloride along with Magnesium Sulphate.

17. in one process, 29o Be' bittern is mixed with 38.5o Be' bittern in such a ratio as to raise the Magnesium Chloride concentration to correspond with Carnallite point. Any further evaporation of the mixed bittern separates Potassium Chloride in bittern as Carnallite.

18. In another process, 36o Be' bittern is heated to above 100o C and its equilibrium gets changed and it becomes unsaturated with respect to Potassium Chloride. This unsaturation is satisfied by mixing it with calculated amount of mixed salt so that Potassium Sulphate is dissolved and Magnesium Sulphate is converted into its insoluble form Kieserite. After removal of insoluble solids, hot slurry is cooled to room temperature and Potassium is crystallised as Carnallite. In Semi- commercial trials at Kandia, the technology was found to be capital and energy intensive. The technology has been modified to Continuous Extraction technique.

19. For extraction of Potassium chloride from Carnallite, it is stirred with a calculated quantity of water at room temperature. Magnesium Chloride dissolves while impure Potassium chloride with 40% Sodium Chloride is separated by Centrifuging. Potassium Chloride is separated by heating impure Potassium chloride with saturated KCL- NACLI solution and heated to 110o C, when Potassium Chloride dissolves while Sodium Chloride is. left as solid residue. The slurry is filtered and allowed to cool to room temperature when pure crystallised Potassium Chloride is separated by centrifuging, dried and packed.

20. Potassium Chloride is separated by flotation to the extent of 58-70% from mixed salt. It has a purity of 96 to 97%. CSMCRI has tried out Potassium Chloride recovery technique in a pilot plant of batch size 10 and 25 kg./ batch. Product quality meets requirement of IS 2779.

21. Potassium Schoenite, a double salt of Potassium and Magnesium Sulphate is prepared by separating Kainite from Mixed salt by flotation technique and converting it to Potassium Schoenite in presence of water. CSMCRI had fabricated a complete plant for recovery of Potassium Schoenite and supplied to Burma and commissioned in May, 1981. The end product quality confirms to IS 6661.

22. Potassium Sulphate is prepared from Mixed salt in three stages. Kainite is obtained by flotation and the floated mixture is treated with water at room temperature to obtain Potassium Schoenite. It is reacted with excess Potassium Chloride to obtain Potassium Sulphate. Recovery is 70-75% with a purity of 95% Potassium Sulphate.

23. CSMCRI has developed a process to prepare high purity Potassium Nitrate 99.5% pure with 90-92% yield utilising Potassium Sulphate, limestone and Nitric Acid as raw materials. The technique has been patented. End product confirms to IS 301 Grade 1 & 2.

24. Regional Research laboratory has work on a process similar to CSMCRI but has tried it at laboratory scale only. Envisaged minimum economic size of plant is 20 tonne per annum. Plant & equipment based on this process is available indigenously.

25. 86.7% of the respondents are aware that Potassium bearing salts can be recovered from bittern. Still none of the Indian Salt producers are presently recovering Potash. Technology not available is the reason cited by majority of respondents, indicating a poor awareness about CSMCRI work on Potash recovery from bittern. Cost and investment data for Potassium Chloride and Potassium Schoenite unit indicate that such units are feasible.

26. Market acceptance is not the problem since most of the Fertiliser units have shown their willingness to use indigenously recovered Potash provided it is competitive in price and meets the required standard specifications. Indian salt industry has high number of small Salt producing units, and collection of bittern at a central place for recovery of Potash is not possible due to wide dispersion of small units. Category 1 units with annual production of more than 50000 tonne are suitable for min. economic size.

27. Natural brine and bittern in Great Rann of Kutch bear good potential for Potash recovery. Land availability is essential for Solar evaporation of bittern to yield Mixed Salt and process it for Potash production. Land utilisation in category 1 units of Indian Salt industry being low, land is available for construction of additional ponds for Potash recovery.

28. Higher Magnesium Sulphate content in bittern generated in Indian Salt industries lead to Kainite type of mixed Salt in place of Carnallite type of mixed salt. Recovery of Potassium Chloride from Kainite is more energy intensive than that from Carnallite. Units abroad have the advantage of low sulphate content in the raw material used by them. CSMCRI technique has been developed considering the high Sulphate content in bittern and is therefore suited to Indian conditions.

29. There are two technology options for recovering Carnallite from bittern Viz. Solar Evaporation and Hot Extraction. The former requires large tract of land for solar ponds but lower energy. Hot extraction technique requires heat input of 75000 to 80000 K. Cal. Per tonne of solution, making it more energy intensive. However, it requires smaller unit area. Necessary equipment and manpower is easily available in India. However, considering availability of surplus land with many organised salt units, former method is preferred due to lower energy and operation cost.

30. Similarly, there are two options for recovering Potassium Chloride from Carnallite viz. Froth Flotation and Hot Crystallisation. Hot Crystallisation has higher yield and purity of the end product but consumes higher energy. Froth flotation process suffers from lower yield and purity but consumes less energy. However, due to purity aspects Hot Crystallisation method is preferred. Potassium Schoenite technique has already been demonstrated by CSMCRI. Cold crystallisation process being used by Arab Potash and Dead Sea Works needs to be developed due to its advantage of low energy cost.

31. Low quantity of bittern generation in majority of Salt units is one of the constraints inhibiting Potash recovery in India. Apart from large no. of small units, even units with large area have poor yield of Salt. Modernisation and mechanisation is essential to improve the present yield of Salt units. Poor awareness about the type of work done by research institutes have also led to poor investment in this sector. Another factor affecting adoption of technology is that research institutes are not geared up to meet the requirement of providing ready to use technology on turnkey basis with performance guarantee. Last but not the least is the conservative attitude of the salt industry, which has been continuing with its old traditional methods and shy of making investments for inducting new techniques.

32.Yet a number of organisations (Appendix B) have shown interest to procure Potash made indigenously; to recover Potash from bittern if viable technology options are made available; and to put up units for Potash recovery with technology tie up or joint venture.

33. Opportunity exists in Kharaghoda to recover Carnallite type of mixed salt from some area where Low Magnesium Sulphate brine is available. Similarly, in Great Rann of Kutch, experiments have proven that natural bittern have potential to yield Potash at Khavda and Gangtabet.

34. Presently Indian salt industry is recovering a very small amount of chemicals from bittern. Based on evaluation of technologies developed in India, review of technologies being used abroad, constraints and prospects of recovering Potash form bittern in India, following recommendations are made:

a) The technique for recovering Potassium Schoenite, a double salt of Potassium Sulphate and Magnesium Sulphate suited for Fertiliser application, is available with CSMCRI. Dialogue may be initiated with Fertiliser companies for marketing of this fertiliser that can also fulfill Magnesium deficiency in soil.

A comprehensive program to grow crops using Potassium Schoenite, as fertiliser is required to be undertaken and its advantages over conventional fertiliser should be established by Government agencies. Only then avenues for its production by Indian Salt producers would bear fruit.

b) The technique for recovery of Potash from bittern has been tried out by CSMCRI on pilot plant basis. Field trials should be carried out in co-ordination with Salt industry to generate data for its widespread commercialisation.

c) Until sufficient data is generated, Potash recovery alone may not appear to be financially attractive at present in India. On the other hand simultaneous recovery of High Purity Magnesium Chemicals, based on CSMCRI technology, would make the overall economics much more attractive and there is a need to coordinate the activities of Industry and Fertiliser Ministry.

d) Sub-soil brine in some part of Kharaghoda is found to have low Magnesium Sulphate content. After extraction of common salt, bittern from such brine can be used to recover Carnallite type of mixed salt. It is simpler and less energy intensive to recover, Potassium fertiliser salts from Carnallite than from Kainite. Detailed study for identification of such areas should be undertaken to assess quantity of sub soil brine that can be utilised for Potash production, annual yield of such brine etc. Further, field trials should be carried out for Potash recovery in this area, using solar evaporation technique.

e) The financial viability of Potash recovery unit should be worked out considering production and marketing of other by-products like Sodium Sulphate, Bromine, which can also be recovered from the same raw material - bittern.

f) Natural bitterns formed in Great Rann of Kutch, is a more concentrated source of Potassium Salts. Past studies have shown Gangta Bet and Khavda area to be promising in this respect. Field trials should be conducted to explore possibility of recovering Potash from this concentrated brine/ naturally formed bittern. Recovery of other chemicals should also be examined simultaneously to put up a Marine chemicals complex.

g) For better co-ordination between Salt manufacturing 'units and Research institutes, a joint committee should be formed having representation of Salt industry, research institutes, and Salt commissioner's office. Such a committee can meet periodically to facilitate identification and sponsoring of research projects by the industry, conducting field trials of technology which are under development/ developed by research institutes and lead to adoption of developed technology the Industry.

h) The licensing of Salt units as a small-scale industry should be reviewed to encourage larger area per salt manufacturing unit. To rehabilitate, small salt producers affected by this, formation of larger co-operative Society of Salt producers should be encouraged.

i) Mechanisation of Salt farms should be encouraged to improve yield in Salt farms. Thus, even with lower area, larger volume of bittern will be generated, which can be useful for economic recovery of Potash and other chemicals from bittern. Mechanisation should also be adopted for Potash recovery production from solar ponds.

j) Recovery of chemicals from bittern would eliminate many harmful chemicals from it. Disposal of bittern should be regulated to protect marine life and groundwater body, and to induce recovery of chemicals from bittern.

k) State & Central government should provide suitable incentives by way Tax holidays/ Exemption of Excise or Sales tax to units recovering Potash from Bittern to encourage industrial units to invest in indigenous development of Potash recovering units.

l) Funds at low rate of interest should be made available to industrialists willing to put up Potash recovery units using bittern as raw material.

m) Fertilisers are subsidised presently to encourage its usage by farmers to increase agricultural output. Similar subsidies should be given to units recovering Potassium fertiliser salts from bittern.

n) Presently, the information about technologies developed, its viability, latest data on its cost of transfer etc. are not widely circulated amongst Salt manufacturing units. Research Institutes should explore mechanisms for free flow of information to Salt industrial units, with the aim of publicising their work resulting in adoption of technologies developed by them.

o) It is essential that solar energy, which is available in Salt producing areas, be used to the maximum extent for Potash recovery so that energy cost is minimised. Wherever surplus land is not available with Salt unit, State government should provide adequate land area for construction of solar ponds for Potash recovery.

Research Institutes should explore possibilities of tying up with Engineering Consultants to provide a complete package of services and provide technology solutions on turnkey basis as desired by the industry.

35. Implementation of recommendations will lead to following benefits and spin offs:

  • Adoption of indigenously developed technology to recover Potash, a chemical of strategic and agricultural importance.
  • Optimal utilisation of bittern - a rich source of chemicals presently not exploited in India.
  • Modernisation and mechanisation will improve yield of the Salt units, which at present are low. More units will be able to recover chemicals from bittern.
  • Increase in production of salt, which would lead to capitalisation of opportunity for export of Salt.
  • Better communication and co-ordination between Salt units and Research Institutes shall lead to development of technologies required by the market and adoption of such technologies.
  • Bittern discharged after recovery of chemicals will have a minimum impact on the environment leading to minimal pollution.
  • Additional revenue generation for Salt manufacturers by income through chemicals recovered from bittern.
  • Conservation of valuable foreign exchange due to indigenous production of Potash
  • Utilisation of surplus land available with some of the salt units
  • Production of other chemicals as by-products adding to the revenue of Potash recovery unit

36. Spin Off benefits:

  • Generation of additional employment opportunities in Potash recovery plants close to Salt areas, which are normally in coastal and backward districts.
  • Generation of economic activity and creation of employment opportunities in downstream industries related to Potash recovery units.
  • Development of backward areas like Kharaghoda and Great Rann of Kutch due to development of Marine Chemical Complexes.
  • Up-gradation of technology in Salt Industry, which has been otherwise using age-old methods for production.
  • Increased revenue in the long run for the Government due to collection of excise/ sale tax on recovered Potash and other chemicals.
  • Possible breakthrough in production of Magnesia in addition to recovery of Potash from bittern

37. In other countries, Potash recovery activity is the primary activity, salt recovery being incidental. In lndia we have to still establish commercial viability of Potash recovery from Sea bittern for which field trials are essential. A joint effort of Research Institutes and the Salt Industry is vital for exploiting this opportunity particularly in Rann of Kutch