Thursday, January 29, 2015


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 such a new height of success for achieving the target of 85,000 viewers of our popular technical blog across the globe today.

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 has 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 provided just below each technical article. We have truly realized that exchanging knowledge has helped us in enriching the knowledge of involved persons.

Trust, we will continue to have your cooperation / supports in future 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.

Kunwar Rajendra

Saturday, December 13, 2014


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. 

Kunwar Rajendra 

Monday, June 2, 2014


Hi Friends,

As discussed in previous articles, about 89% of alumina produced in the World is used for manufacture of aluminium metal and remaining 11% for production of chemicals and other non-metallurgical applications. Thus calcined alumina as well as hydrated alumina (Hydrate) is broadly characterized in two categories-
  •       Metallurgical grade alumina or Smelter grade alumina (MGA or SGA)) and
  •       Non-metallurgical grade alumina or Chemical grade alumina (NMGA or CGA).
Though the volume of CGA market is less compared to that of SGA but the profit margin in CGA is much higher as its selling price ranges from 2 to 5 times of that of SGA. Presently, the market potential of CGA across the globe is estimated at around 5.8 to 6.0 million tonnes per annum. Out of total CGA demand in International market, specialty grade hydrates have market share of over 50% i.e. about 3.0 to 3.2 Mtpa being used as feed stock for manufacture of Aluminium sulphate, Fire retardant fillers, Tooth paste, Sealing rings for rotating equipment, Thread guides, Polish, Paints, Ceramics, Abrasive, High temperature refractory and American diamond. During last couple of years, selling price of CGA has shown increasing trend along with increase in its demand whereas selling price of SGA has shown downward trend hovering at the level of US$ 350-360 per tonne of calcined alumina because of lower LME price of aluminium metal. Now, let me give the brief account of bauxite reserves and alumina scenario with more focus on salient features of Alumina projects in Indonesia in subsequent paragraphs.

As per data available on public domain, bauxite is available in Tayan, Munggu Pasir, Mempawah and West Kalimantan region in Indonesia. West Kalimantan is having total bauxite reserves of over 2000 million tonnes with proven reserves of over 800 million tonnes of bauxite. The bauxite is predominantly gibbsitic in nature with average quality of about 43% total alumina, about 38.6% available alumina and around 3% reactive silica. The bauxite in Indonesia has been seen in low lying hills with overburden varying from 0.60 m to 3.8 m and nodular bauxite horizon from 2.2 to 5.2 m. The geographical studies indicate that these bauxite deposits were formed by in-situ weathering. Till last year, the country was exporting bauxite to china and other countries but in the recent past, the Indonesian government has totally banned the export of bauxite and putting more focus on processing of bauxite for production of value added products.

In Indonesia, there are two major Alumina projects in West Kalimantan namely Tayan Alumina Project and Mempawah Alumina Project under execution and active consideration as outlined here under.

Tayan CGA Project: Tayan bauxite mine commenced its operation in early 2010 and was exporting bauxite to China and Japan. Construction of Tayan Alumina Project was started in April 2011 aiming to mechanical completion schedule in December 2013 and trial production in January 2014. The capacity of this plant is 0.300 million tonnes for production of wide varieties of Chemical grade hydrates and aluminas. The estimated project cost is US$ 490 million with the technology supplied by Showadenko (SDK), Japan. The actual mechanical completion of this project is expected by end of December 2014 and commercial production by March 2015.

Mempawah SGA Project: The capacity of this plant is 1.2 million tonnes of SGA to be supplied as feed stock to Aluminium Smelter. The estimated capital investment will be about US$ 1.5 billion. The construction of this plant will be started by early 2015 with mechanical completion target of December 2017.

Both Alumina projects have promising future because of locational advantages, availability of good bauxite reserves, adequate coal reserves and adoption of advanced technology. I wish grand success of both projects.

We seek your valued comments / opinions / additional information, if any.

Kunwar Rajendra

Wednesday, August 21, 2013

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.

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.

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.

Kunwar Rajendra

Friday, July 26, 2013

Reasons for Coloration in Product Hydrate & Corrective Measures to Improve Whiteness & Brightness

Hi Friends,

First, we would like to share the background of this technical blog. Till the end of 20th century, generally people were reluctant to share their technical knowledge particular on hydrates and alumina. In the back of their mind, it was a general feeling that only a few have particular data / information. But the advancement in communication technology revolutionized the knowledge sharing approach. In order to get advantages of technology and knowledge sharing approach among bauxite, alumina and aluminium professionals, we started this specialized technical blog couple of years ago with aggressive impulse and approach for achieving the difficult goal set by involved team of professionals. Fortunately, we could maintain the accelerated pace so far with our keen interests, enthusiasm and pleasure in publishing wide range of 273 technical articles pertaining to bauxite, alumina and aluminium. Now, when we look back towards the trajectory of our progress path traveled so far , we find that we have surpassed all our targets and goals well ahead of our planned schedule without compromising on quality. This reflects the grand success of one and all associated with this technical blog. Till date, we have more than 60,000 members and 75 Key Members who are closely connected who made their contribution by way of sharing their knowledge, data and information of public domain nature through this unique platform / web site. Today, we are ourselves astonished on our achievements of set goals. On the eve of this grand success day, we would like to express our sincere thanks to renowned Alumina Expert, Mr. George Banvolgyi of Hungary, for his blessings, guidance, inspiration and support during our journey of publishing variety of technical papers on this technical blog. Everybody deserves applaud and congratulations on this eve for bringing this platform to a new higher level of popularity. It gives me immense pleasure to be associated with this site as the founder member among the friends of bauxite, alumina and aluminium fraternity.Our each tiny achievement is the outcome of our efforts and as we consider it as the golden gift of God and hence we must celebrate the same with full enthusiasm and happiness. On similar lines, on achievement of every thousand of added viewers of our technical blog, we make our efforts to publish at least one special technical article on every special occasions. 

Today, we have achieved the total viewers of 60,000 with 76 Key Members across the globe closely associated and contributed in the grand success of this specialized technical blog. This day will definitely remain memorable for all of us and particularly for each member of bauxite-alumina-aluminium fraternity. All viewers and key members of this technical blog deserves congratulations on the eve of this new height of success as every body has contributed directly or indirectly in achieving this sky high target. On this great occasion, we are publishing this unique and special technical article for value addition to product hydrate by making it dazzling white and bright adopting corrective measures in process steps as described here under.

There are several grades of Hydrated alumina (Hydrates) manufactured and marketed across the globe. These hydrates are generally known as Specialty grade hydrate or Non-metallurgical grade hydrate. These are marketed at 2 to 5 times the price of Standard chemical grade hydrate. It has been seen practically that over and above desired chemical composition, brightness or whiteness of hydrates has premium market. Thus it becomes important to address the issue of coloration of hydrate and remedial measures for improving the whiteness so as to add more value to it. 

In present post, we will briefly cover the most probable reasons for coloration of product hydrate and appropriate technical solutions as remedial measures to improve whiteness and brightness as well.

There are two main reasons for coloration in product hydrate and appropriate solutions opined by many process experts as described here in subsequent paragraphs-
  1. High soda content in product hydrate
  2. High suspended solids in Thickener overflow pregnant liquor.
Step-I: With our experience in different Alumina refineries in the World, we have experienced the high soda content in product hydrate as one of the basic reasons. The identification of this issue is confirmed through simple analytical technique by analyzing the Na2O content in product hydrate ready for dispatch to respective customers. If total Na2O content in Hydrate is found more than 0.30% then it confirms that Hydrate generated in precipitators / decomposers / crystallizers has not been washed properly on product filter wherein the maximum component of leachable soda is removed. After observing this high soda content, vigorous washing of hydrate using steam /  hot water at temperature around 95-98oC helps in achieving total Na2O content below 0.30%. This step easily improves the product whiteness. For further improvement on washing efficiency, steam-hood at the discharge side of product filter can also be considered.

Step-II: High Fe2O3 content in product hydrate above 0.010% is the key indication of high suspended solids in filtered aluminate liquor feeding to Decomposers (Crystallizers / Precipitators). The suspended solids must be controlled below 15 mgpl (i.e. 15 milligrams per litre of pregnant liquor) in feed to Decomposers. Higher solids in pregnant liquor happens because of inadequate settling of suspended red mud particles in Liquor thickener for the major reasons listed below-

(a) High generation of fines during grinding of Bauxite:  Control fineness of Bauxite at optimum level to ensure higher settling rate of red mud particles in thickener. Generally, minus 60 mesh fraction in ground bauxite slurry is maintained more than 85%. Check and control it accordingly.

(b) Higher viscosity of thickener overflow liquor because of its lower temperature: Temperature of Thickener overflowliquor must be controlled at around 100-102 degree C if  the concentration of liquor in thickener overflow is at around 140-145 gpl Na2O or above. High concentration profile is the need of modern Alumina refinery in order to have improved productivity so as to minimise thermal and electrical energy consumption.

(c) Selection of right settling agent: Settling agent used for faster settling of residue particles play vital role in achieving desired quality of product. There are different types of natural and synthetic high density polymers are available for different application. It has been observed that mixed natural starch with particular type of synthetic floccullent are  cost effective for Alumina refinery. 

(d) Selection of proper filter cloth for polishing filtration equipment: Selection of proper filter cloth is equally essential for controlling suspended solids in filtered aluminate liquor fed to crystallizers. Polypropylene filter cloth of more than 30 and 32 EPI and PPI have been found to be the most suitable cloth for security filtration.

(e) Controlling ingress of P2Ocontent in Bauxite: At times, high P2O5 content in Bauxite affects the settling rate of residue (Red mud) in thickener. To eliminate this issue, start adding small quantity of Burnt lime (CaO) in Bauxite being fed to Grinding mill. This results in reducing the Phosphorus content in liquor forming Calcium Phosphate.

(f) Control Filter feed pressure below 2.0 kg/cm2.g: Lower the fitration pressure better is the filtrate quality. Pressure around 2.9 kg/cm2.g has been found to be optimum.

(g) Control solids in Thickener overflow Liquor well within 100 mgpl: Suspended solids in feed liquor to filter should be controlled well within 100 mgpl so as to avoid extra load of residue on polishing filtration unit thereby improving the filtrate quality to crystallizers,

(h) Optimize dosing of TCA: TCA (Tri calcium aluminate) addition to filter feed liquor results in improved fitrate quality. It has been established in various plants across the globe that mass flow of TCA equal to 10 times of suspended solids in Thickener is optimum.

Step-III: Check & Replace Security Filters in Service: Even after checking and monitoring all the above mentioned parameters stated under Step-I & II, if there is no appreciable improvement in filtrate clarity, then it concludes that some thing wrong with filtration equipment itself. In such situation, replacement of Polishing filters with suitably sized and designed security filters is the ultimate solution to this problem. Since this step requires additional capital expenditure fot the plant, thus decision needs to be taken only after thorough investigations of results obtained during Step-I and Step-II under the guidance of process expert who has operated the similar systems in any Alumina refinery across the globe.

Aluminium Trihydrate
Trust, all major possible reasons for poor filtrate clarity have been covered here and desired solutions have been presented with utmost care. In case, we have missed out any major reason, please come forward and put your views under Comments just below the article. Our team of experts will welcome your valuable comments / remarks in the benefit of readers across the globe. Everybody will like to have hydrated alumina with whiteness and brightness as shown here in the pictorial view. The major chemical constituents and coarseness / fineness are given below-
Fe2O3: 0.007%, SiO2: 0.007%, Na2O:0.23% and Minus 45 microns: ~ 90%. This hydrate is the basic input material for producing American Diamond for jewelry, Thread guides, Sealing rings for pumps and many other valuable products. The author was deeply involved in development of this product, project engineering, trial run and manufacture of this product in the plant. Thus, if you can feel this product, you can definitely produce it in your own plant. Trust, our learned friends of alumina fraternity will put their valuable remarks and opinions under comments paragraph which will help in enriching our knowledge base towards our approach and methodology in achieving better results in future. Your views / remarks / comments matter for us for improvements in forthcoming articles. Please never be hesitant in expressing your opinions. We seek your continued support and welcome your suggestions.

Kind regards.

Kunwar Rajendra

Tuesday, May 14, 2013


Hi Friends,

We congratulate all members of bauxite-alumina-aluminium fraternity for setting a new height of success by achieving the target of 56,000 viewers of our popular technical blog today, the 15th of May 2013. We are thankful for your continued support, feed back and contribution in improving the quality of technical articles published on regular basis.

We celebrate every success and thus it was essentially felt to express our views on this grand occasion.

Let us keep contributing in future for further improvements.

Kunwar Rajendra

Tuesday, March 5, 2013


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.

                        Kunwar Rajendra