CONGRATULATIONS TO ALL MEMBERS OF BAUXITE-ALUMINA-ALUMINIUM FRATERNITY !

Hi Friends,

Our efforts of exchanging our knowledge on the technical platform of Alumina Technology blog has fetched us to a new height of success. All of us who contributed directly or indirectly in achieving this grand success deserves our heartiest Congratulations! We congratulate all members of bauxite-alumina-aluminium fraternity for setting up such a new record of of success in achieving the target of 95,000 viewers of our popular technical blog across the globe today, the 19th June 2015.

The editorial team of Alumina Technology blog is thankful to you all of you for your continued co-operation, support, feed back and contribution in improving the quality of technical articles published on regular basis.

We celebrate every success and thus we are now aiming for the grand occasion for reaching to  a further milestone of success to cross the total viewer target of 100,000 within couple of months from now. We have observed that our younger generation of bauxite-alumina-aluminium fraternity have started taking keen interest in analyzing the articles with due care and expressing their views and suggestion by putting their remarks in the space provided under "Comments" column located just below each technical article. We have truly realized that exchanging knowledge has helped us in enriching the knowledge of all involved persons.

Trust, we will continue to have your cooperation / supports in days to come for further improvements in quality of articles published on this blog. Your comments encourages our team to be more careful while publishing any new article on this popular technical platform. Knowledge sharing, positive attitude towards our assignment and improving skill are the key to success. Let us remember these tools of success for achieving our goals.

Regards

Kunwar Rajendra

PROCESS CALCULATIONS FOR 10,000 TPA ZEOLITE- A PLANT

Hi Friends,

In earlier post, we have already discussed about the specifications, applications and market potential of Zeolite-A. In present post, we will concentrate ourselves on basic theory and principles to develop most economic production process route and also present basic calculations involved in production of Zeolite-A after analyzing the pros and cons of various process routes using hydrate and bauxite as the basic input material along with sodium silicate.  

Process and Involved Reactions:

Zeolite-A is chemically represented as Na₁₂(AlO₂)₁₂(SiO₂)₁₂.27H₂O. It is evident from  its chemical formula that one mole of sodium aluminate and one mole of silica will be required along with 27 moles of water for production of one mole of Zeolite-A. In other words, combination of one mole of alumina with one mole of silica will produce one mole of Zeolite-A in presence of sodium hydroxide.

As highlighted in earlier post, bauxite based Zeolite-A plant is more profitable as bauxite is the cheaper source for generating sodium aluminate which in turn result in production of Zeolite–A with aqueous sodium silicate. In this process, alumina present in bauxite forms sodium aluminate on heating with NaOH and reactive silica present in bauxite will get converted to sodium silicate on combination with caustic soda as per following reactions-

Al(OH)₃ + NaOH = NaAlO₂ + 2H₂O.

SiO₂ + 2NaOH = Na₂SiO₃ + H₂O.

In further steps, sodium aluminate on reaction with sodium silicate will result in formation of Zeolite-A as shown in following reactions-

12NaAlO₂ + 12Na₂SiO₃ + 12H₂O = Na₁₂(AlO₂)₁₂(SiO₂)₁₂ + 24NaOH

Na₁₂(AlO₂)₁₂(SiO₂)₁₂ + 27 H₂O = Na₁₂(AlO₂)₁₂(SiO₂)₁₂ .27 H₂O

Estimated Input Material Requirement:

The above reactions clearly reveal that twelve moles of hydrated alumina and twelve moles of sodium silicate in aqueous solution produce one mole of Zeolite-A.

Molar mass of Hydrated alumina = 27 + 3*(16+1) = 78 g per mole.

Molar mass of Sodium silicate = 2*23 + 28 + 3*16 = 122 g per mole.

Molar mass of Zeolite-A =12*23+12*(27+2*16)+12*(28+2*16)+27*18 = 2190 g per mole.

∴ Required Hydrate with 10% moisture = (12*78)/(2190*0.90) = 475 kg / t Zeolite-A.

Required Sodium Silicate = (12*122)/2190 = 668 kg/t Zeolite-A.

About 1% physical NaOH and 0.50% occluded NaOH will be lost per tonne of Zeolite-A.

∴ Loss of NaOH with product =1.5%*1= 0.015 t NaOH =15 kg NaOH per tonne of Zeolite-A.

Loss of NaOH with Bauxite residue = 10 kg per tonne of Product.

Chemical losses because of Reactive SiO₂ = 30 kg per tonne of product,

Physical losses of NaOH during production = 10 kg NaOH per tonne of Zeolite-A.

Thus total requirement of NaOH=15+10 + 30 + 10 = 65 kg NaOH per tonne of Zeolite-A.

Annual Requirement of Raw materials for 10,000 tpa Zeolite-A Plant:

Hydrate with 10% moisture = 4750 tonnes.

Sodium Silicate = 6680 tonnes,

Caustic soda as NaOH = 650 tonnes.

As such, the above elaborations are brief guidelines for the plant designers of Zeolite-A plant. These are the basic clues based on which development of plant design, basic and detailed engineering activities can be taken up to initiate the execution of project of optimum production capacity.

Trust, you will find these basic inputs as interesting. Please do not take any investment decisions based on the technical inputs published on our blog without carrying out techno-economic feasibility studies. The market for synthetic Zeolite-A is very fluctuating as China is dumping natural Zeolite in nearby countries so you may not get price advantage in present scenario. But for future, Bauxite based Zeolite plant may be a good project having pay back period for investment less than three (3) years.

We will welcome your comments / feed back on the subject for further improvements. 

Regards.

Rajendra Kunwar
rajendra@ceti.co.in
www.ceti.co.in

Bauxite : A Major Concern for Chinese Alumina Refineries

Hi Friends,

All of us are well aware that China has added the Alumina refinery capacities at faster pace during last decade though they have the limitation of quality bauxite for processing at economic level. Chinese bauxite is poor in quality as it has diasporic alumina coupled with very high reactive silica.

It will be prudent to mention here that diasporic alumina extraction is highly energy intensive and high reactive silica in bauxite causes higher Caustic soda consumption for alumina production. Also, the mining cost of bauxite in China is comparatively higher compared to other countries. Thus, imported bauxite from neighboring countries is mixed with locally mined bauxite before processing in plants. Following details will make the elaboration easy for understanding. 

Current production cost of calcined alumina in China is ranging from US$320 to US$380 per tonne of calcined alumina. The broad break up of cost components are outlined below-

• Bauxite : US$90 to US$170 per tonne of alumina
• Caustic : US$50 to US$60 per tonne of alumina
• Energy  : US$140 to US$180 per tonne of alumina
• Others   : Us$50 to US$60 per tonne of alumina.

Among Chinese Alumina refineries, Guangxi Alumina Plant has the lowest production cost at around US$320 per tonne of calcined alumina. However, production cost at Shandong Alumina Plant in China works out to around US$380 per tonne of calcined alumina.

The data published data clearly reveal that Indonesia had been the largest exporter of bauxite to China. In the year 2012, Indonesia exported over 36 million tonnes of bauxite to China where as the balance bauxite of about 9 million tonnes was exported by Australia, India and other countries.

Now, Indonesian Government has increased the export tax from 20% in 2012 to 50% in 2013-14. Also, the government has announced complete ban on export of bauxite from 2014 onward as they have decided to preserve their natural resources for the existing and upcoming Alumina plants in their country. The article on "Promising Alumina refinery projects in Indonesia" may be of interest to you.

Looking at the above scenario, it has become a very serious issue for China to keep their plants operative in years to come. Presently, China is consuming its total domestic alumina in their own Aluminium smelters for production of aluminium metal. 

In present crisis of bauxite availability from Indonesia, China is exploring the possibility to import bauxite from Guinea. But higher transportation cost of bauxite from Guinea will make the production cost further higher for production of calcined alumina in China.

Further, to enhance your data base, you may be interested to read Benchmark figure of Energy Consumption in Alumina Refinery.

We have assimilated the above information based on the published literature available on public domain in the interest of our friends of bauxite-alumina-aluminium fraternity across the globe.

We solicit your comments / remarks, if any.

Rajendra Kunwar 
rajendra@ceti.co.in
www.ceti.co.in

BENEFICIATION OF BAUXITE FOR ENRICHMENT IN QUALITY

Hi Friends,

In continuation to my earlier posts, I thought of sharing my views on beneficiation of Bauxite with the objective to optimum utilization of natural resources available with us. I am presenting here my views on the subject as outlined here under in subsequent paragraphs.

The mineral, Bauxite, is a rich source of alumina for making aluminum. The aluminium metal and its alloys have strong growth potential in international market for wide range of industrial applications. Bauxite is also used in refractory, cement, absorbents, steel, abrasives, rubber, plastic, cosmetics, paints, paper, polishes, glass, enamel and ceramics.

Since bauxite is a mineral occurring in earth’s crust, it has a number of impurities, like iron, silica, titania, calcium, and small quantities of phosphorous, sulfur, zinc, magnesium and various carbonate and silicate minerals. These impurities create quality problems during processing thereby increase production costs. Therefore, the removal of impurities to the extent possible economically is essential before processing further for any application.

Most mines abroad subject their run of mine ore (ROM) to the mineral dressing operation most suitable for their material. Crushing the ROM, usually in hammer mills, is an operation practiced worldwide. Depending on the bauxite, and the quality/grade required, the next stages are screening, scrubbing and washing, magnetic separation and drying. Magnetic separation is done to remove iron, however, is normally practiced in a limited way to produce high value, special grade bauxites. At present, the production of bauxite in most operative mines in India is not sufficiently high as to warrant a capital-intensive beneficiation plant, which usually requires a large capacity to be really economical. Hence, ore dressing efforts have been mainly confined to removal of silica by manual and/or mechanized breaking, crushing, manual sorting and dry screening.

Efforts towards research are being emphasized in most bauxite producing countries to develop cheap and innovative bauxite beneficiation processes. Many new methods of magnetic separation are also being tried out. These include rare earth roll separators, super conducting high gradient magnetic separators and open gradient, non-cryogenic high gradient magnetic separators. Other methods being researched include fluidized bed acid leaching, hydrogen assisted beneficiation and bio leaching. However, despite decades of intensive studies, economical bauxite beneficiation technology for removal of impurities satisfactorily is not available as on date.

Research in India is along international lines but still confined to the laboratory. The Indian Bureau of Mines, Nagpur (IBM), the Jawaharlal Nehru Research Development and Design Center, Nagpur (JNARDDC), and the Regional Research Laboratory, Bhubaneswar (RRL), all claim to have laboratory scale processes that are ready to be up scaled to pilot plant levels. The IBM has done numerous beneficiation tests, using different methods, on various bauxites found in India. The RRL claims to have developed a beneficiation process to produce non-metallurgical grade bauxite, whereas the JNARDDC says it has processes for both metallurgical and non-metallurgical grades.

As per the available published literatures and analysis, the savings on raw ore cost brought by JNARDDC's process through beneficiating metallurgical grade bauxite appears to be over 17% and that of non-metallurgical grade at least 19%. Bauxite users in India have indicated that they are willing to pay between 10-50% higher for a reduction in impurities by a similar amount. This would make the production and marketing of beneficiated bauxite more profitable.

We will welcome your comments / remarks on the elaborated topic.

Regards.

                        Kunwar Rajendra

Operational Sequence for Start up & Commissioning of Alumina Refinery

Hi Friends,

In present post, we will discuss the operational sequence for starting and commissioning of Alumina refinery. As such, there may be many permutations and combinations of operational sequence for starting and commissioning of Alumina refinery. We are presenting here one of them which may be simple and most appropriate. The schematic diagram is presented here under-

Start up and commissioning of Alumina refinery is taken up after following activities-

• Thorough checking for Mechanical completion,
• Readiness of raw water supply system and DM plant,
• Synchronization of boilers and turbo-generators,
• Cold water run and 
• Hot water run.
• Ensuring the availability of adequate input materials.

Caustic concentration build up and raising its temperature to around 85 degree centigrade are pre-commissioning activities required for start up of Alumina refinery. Sequence of caustic concentration build up, temperature raising, start up and commissioning steps are taken up in following sequence-

1. Fresh caustic lye received by road / rail tankers are stored in Caustic storage tanks (CSTs) and 6 or 7 nos. precipitators of 2nd line as 1st line precipitators shall be taken into range for commissioning.
2. Initially, Evaporator feed tank, Liquor preparation tank, Digesters, Flash tanks, Heaters and one of the Decanters are taken into range for concentration build up and temperature raising. Accordingly closed circuit with these equipment is made by temporary connections for circulation of liquor before start up. 
3. Water is taken in Evaporator feed tank through temporary lines and operation of evaporator is initiated at low vacuum and operation is stabilized slowly with boiling. This ensures the adequate condensate supply to boilers as well as hot water for dilution of caustic lye to around 150 to 200 gpl caustic in Liquor preparation tank. 
4. Run the Test tank pump at about 50% flow for filling Heaters, Digesters and Decanter connected in the circuit. Keep the drain valves of Heaters in open condition in the beginning  for purging out entrapped air in pipelines otherwise it may cause damage to chambers of heaters.
5. Open steam in Live steam heater maintaining the outlet temperature below 100 degree centigrade. 
6. Circulation of liquor in this circuit is continued for about 24 hours for checking the readiness of process circuit.
7. Start Bauxite charging to grinding mill at about 50% digestion liquor flow and taking charging ratio at around 0.300. Bauxite charging to grinding circuit is considered as start of plant commissioning i.e. Zero hour of plant commissioning.
8. Two desilication tanks will be filled up with slurry taking Bauxite slurry heaters into service. After attaining about 16 hours of desilication time, temporary circuit of Red area will be discontinued and permanent process circuit will be energized for generation of spent liquor.
9. Start flocculent preparation and dosing to settler as required.
10. Initially Security filters will be operating as a spool but will be taken into range afterwards for ensuring required purity of plant liquor.
11. Heat Interchange Unit will be kept bypassed and filling of precipitators shall be started taking only five (5) precipitators in range for the purpose of adequate seed generation.
12. Continue circulation of Precipitation liquor through Evaporators and Digesters for slowly raising the temperature profile of liquor.
13. Slowly increase the digestion liquor concentration to around 250 gpl caustic and step up charging ratio to around 0.620 level for raising the ratio profile of aluminate liquor to the level of pregnant liquor. 
14. Take Residue washers into circuit.
15. After attaining the aluminate liquor ratio above 0.600 in feed liquor of Precipitation tanks, start seeding with purchased solid hydrate at controlled rate for generation of seed hydrate. For the purpose, solid hydrate will be mixed in Seed mixing tank with Pregnant liquor and pumped to those five (5) Precipitation tanks taken in range.
16. Maximize charging ratio to the desired saturation level and increase Bauxite charge at increase digestion liquor flow.
17. Hydrate generated in Precipitation circuit will be used as seed till adequate hydrate is built up in the process.
18. Discontinue all temporary connections and continue operation as normal by taking desired number of equipment and vessels of one line of process circuit.
19. Start hydrate classification circuit and transfer of product hydrate to Hydrate storage shed.
20. After making a stock of about 20,000 tonnes of hydrate in storage shed, commission Calciner for production of calcined alumina.
21. Stabilize plant operation for maximizing alumina production level.

Hope, starting and commissioning procedure for Alumina refinery has been covered with clarity in understanding.

Please put your views / suggestions / remarks / comments, if any.

Regards.

Kunwar Rajendra