Advanced Decanter Centrifuge Designed for Bauxite Tailings Management

• Customization: Available
• After-sales Service: 24 Hours on Line
• Warranty: 12monthes
• Model NO.: LW
• Type: Separating Plant
• Separation Mode: Sedimentation Type
• Operating Type: Continuous Type
• Installation: Horizontal
• Centrifuge Type: Horizontal Spiral Centrifuge
• Pressure: Low Pressure
• Condition: New
• Material: SS304 or SS316 L
• Motor: ABB
• Touch Screen: Siemens
• Inverter: ABB
• Transport Package: Wooden Cases
• Specification: 2065*1050*800
• Trademark: SHENZHOU
• Origin: Zhejiang
• HS Code: 8421192000
• Production Capacity: 500sets
• Package Size: 105.00cm * 80.00cm * 160.00cm
• Package Gross Weight: 1050.000kg

Product Description

Depending on the ore quality, a washing process can be conducted with the bauxite, which basically consists of scrubbing the ore and screening in order to increase the available alumina grade, i.e., the alumina extractable using the Bayer Process, and reduce the impurity content. Tailings are usually disposed of in a tailings dam in the form of a slurry, which is a mixture of solid particles and liquid, consisting mainly of ultra-fine kaolinite, making the dewatering operation challenging. To reduce the environmental impact, mining companies are studying alternative methods to dewater the tailings, and different dewatering methods are available worldwide. The use of new technologies to dewater the tailings has contributed to facing the challenges of achieving sustainable development with their disposal. The decanter centrifuges are already an option for operations for the Canadian oil sands, gold ore in Peru, and nickel in New Caledonia; they are also being tested for iron ore in Brazil. In the present work, bauxite dewatering using the decanter centrifuge was evaluated to understand more about the behavior of these materials and to investigate the effects of various process parameters on the solid recovery and solid content of the flows, using three different kinds of equipment. The results indicated that decanter centrifuges can be used to achieve a high concentration of solids in the cake, with values ranging from 60% to 80% solids per weight and a great clarification in the liquid phase (centrate) from 0 to 6% solids per weight, values which mean the solid phase is suitable for reutilization in the processing circuit. Additionally, the present work provides a better understanding of how different solid contents feed can affect the behavior of the equipment.

 

About 8% of the Earth's crust comprises aluminum, the most abundant metal in the world. It is considered a metal of the future due to its strategic significance, and bauxite is the only ore commercially used for extracting aluminum metal [1].

The world's bauxite reserve is around 33.4 billion metric tons. Brazil accounts for 3.5 billion metric tons of these reserves, of which 95% is metallurgical bauxite. Around 95% of production is used to obtain metallic aluminum, through the Bayer process, followed by the Hall-Héroult process [2].

Bauxite consists of hydrated aluminum oxide in the mineral form of gibbsite, bohemite, and diaspore, with a significant number of impurities such as silica, iron, titanium, and other minerals in smaller proportions. After bauxite mining, depending on the ore quality, a washing process can be conducted, in which the bauxite ore is scrubbed and washed in order to increase its available alumina grade, i.e., the alumina extractable using the Bayer Process, and reduce the impurity content. Among the impurities, the most harmful for the Bayer Process is the reactive silica, i.e., the mineral which increases caustic soda consumption, increasing production costs and causing environmental concerns due to the generation of large volumes of tailings [1,2,3,4].

According to Hansen et al. [5], raw materials are vital for economic development and the well-being of populations, and society is therefore dependent on their abundant supply. Aluminum production has a range of impacts, including environmental impacts such as greenhouse gas emissions, huge energy consumption, dust pollution, and changes in the landscape and neighborhoods due to the management of the tailings produced in the process. Figure 1 shows the number of academic publications about different types of impact, with environmental impacts clearly constituting the greatest number of publications, over the 40-year period covered by the search, from 1983 until 2023.

Figure 1. Number of academic publications concerning different impact types in the aluminum industry

Bauxite tailings are usually disposed of in tailings ponds in form of a slurry, which is a mixture of solid particles and liquid; this not only increases the economic burden of the alumina production enterprises, but also occupies large amounts of land, posing a serious threat to the surrounding air, soil, and water resources, and may cause leakage accidents at any time, which are one of the greatest sources of environmental impacts concerning bauxite processing. To mitigate these environmental impacts of the aluminum industry, several mining companies are studying alternative methods to dewater the tailings prior to their disposal or dry stacking them, but they are also studying methods for tailing thickening, tailing storage, and tailing utilization 

This new approach is very positive in terms of minimizing the intensive demand for large dams or ponds and reducing their environmental impacts. The methods used for disposing of the tailings have been developed due to environmental pressures, which are becoming more serious with the increasing exploration of lower-grade deposits The use of new technologies for dewatering the tailings has contributed to facing these challenges and achieving sustainable development with their disposal  Centrifuges, specifically the decanter type, are a versatile piece of equipment, with the advantages of continuous production and high dewatering efficiency .

The decanter centrifuge has become a major processing tool in a wide range of liquid/solid separation applications. It is a piece of dewatering equipment, the main characteristic of which is the use of centrifugal force, which acts on solid particles with an intensity much greater than the gravitational force and that can be multiplied by increasing the rotation speed . Figure 2 shows a schematic view of the decanter centrifuge. The products are a high solid content, a "cake", and a liquid product, named "centrate".

Figure 2. Cut-away of solid bowl decanter centrifuge 

The efficiency of a decanter centrifuge is largely connected with the centrifugal force, feed rate, and weir diameter, as well as the characteristics of the solid particles themselves. As decanter centrifuges can be easily adjusted to different operation requirements, they are used for a wide variety of applications and different industrial branches, such as wastewater treatment, the refining and dewatering of petrochemicals, mineral processing, and vegetable oil and dairy processing .

For a successful scale-up to industrial-scale, experiments on a pilot scale are recommended to determine the correct transfer function and hence map the non-linearity of the system in decanter centrifuges. This has the disadvantage that a significant number of experiments is often necessry, which implies a high energy demand, personnel, and cost expenditure.

In a tailings dam, solids are settled using sedimentation, so that the force on the particles is the Earth's natural gravity. However, when the percentage of particles below 37 µm in the tailings is about 90%-100% and the percentage of solids (volume basis) in the slurry is high, the settling rate is very low due to the high viscosity of this kind of slurry. In these cases, prior dewatering becomes an interesting option. Bauxite tailings fit in this case, given that in their processing, all the fine fraction is considered tailings, and the goal of this research is to gain a better understanding of the segregation and settling behavior of bauxite tailings.

This study aims to evaluate the results of decanter centrifuges for dewatering bauxite tailings from the bauxite deposits in the southeastern region of Minas Gerais State, Brazil, with the intention to develop and to optimize a dewatering system for the bauxite tailings. To describe its geological formation in brief, the ore is from the NE-trending belt that begins in São João Nepomuceno and continues to Espera Feliz, with interruptions mainly in the valleys of rivers Pomba and Muriaé.

The present study is relevant not only due to the increasing governmental and social pressures regarding tailings dams, but also due to environmental incentives for using alternative methods for dewatering tailings and, furthermore, mitigating a scarcity of literature on the topics of dewatering bauxite tailings and the use of decanter centrifuges for dewatering tailings.

 

2. Challenges in Tailing Reprocessing
Reprocessing tailings presents several challenges:

• Fine Particle Separation:Tailings contain fine particles, making it difficult to separate valuable minerals from waste materials using conventional methods.
• Water Management: Tailing reprocessing generates large volumes of slurry that must be dewatered efficiently to minimize water usage and ensure regulatory compliance.
• Environmental Concerns: Tailings are often acidic or contain harmful chemicals, requiring effective treatment before disposal or reuse.

A decanter centrifuge addresses these challenges by providing efficient dewatering and separation of fine particles, reducing the volume of waste and optimizing water recovery.

Experimental trials were performed with tailings from the bauxite washing plant in three decanter centrifuges of different manufacturers and sizes. The separation of the phases depends on decanter design and different operating variables, including the centrifugal force exerted on the feed, the pond depth, the differential speed, and the flow rate.

For scale-up purposes, tests should be performed in a pilot plant through the steps seen in Figure 4.

 

The pilot plant is composed of the following main equipment:

• A sizer-type crusher, with an opening of 50 mm;
• A slurry chute that uses high-pressure jet technology to promote disaggregation of the clay particles on the bauxite particles;
• A sieve with 1 mm screen;
• Decanter centrifuge.

The three decanter centrifuges tested had different operational variables, such as bowl rotating speed, differential speed, and total length, as shown in Table 1.

Table 1. Geometries of centrifuges tested in the present work.

 

Samples of feed, cake and centrate were collected at the points illustrated in Figure 5.

The decanter centrifuge feed flow (point #1) is essential for closing the mass balance. Information on flow rates and densities at this point are essential and recorded at each aliquot collection. For sampling the flow, the following protocol was followed:

• Sample the slurry at the feed of the centrifuge, taking 1 aliquot of 2.5 L at every 20 min of operation, with at least 3 aliquots per test;
• Minimum operating time of 1 h straight per condition.

Collecting the cake sample (point #3) is the most difficult step to carry out, and the accuracy of representation in this experiment is a major uncertainty in this study. For sampling the flow, the following protocol was followed:

• Sample at the top of the dewatered clay pile to obtain an aliquot of 10 kg every 20 min of operation, with at least 3 aliquots per test;
• Minimum operating time of 1 h straight per condition.

Finally, the centrate flow sample (point #2) is another flow essential for closing the mass balance. Information on flow rates and densities at this point are essential and recorded at each aliquot collection. For sampling the flow, the following protocol was followed:

• Sample slurry at the clarified pumping outlet, obtain an aliquot of 7 L every 20 min of operation, with at least 3 aliquots per test;
• Minimum operating time of 1 h straight per condition.

For determining the density of the slurry, the Marcy scale was used based on Equation (1). Densities of the ore and liquid were assumed to be 2.5 g/cm³ and 1.0 g/cm³, respectively.

 

• Ds = solid (ore) density;
• Dp = liquid density.

The Marcy scale is composed of a scale and a stainless-steel container with a volume of 1000 cm³ (Figure 6), and is a practical and widely used piece of equipment in the operations of mineral processing plants, being used to measuring the density of slurry, solids, and liquids with quick readings, without the need to use graphs or abacus, or perform calculations .

Model	Technical parameter					motor power		outline dimension(mm)	Machine weight (KG)
	(Diameter)mm	Rotation speed rpm	Length mm	Separation factor G	capacity M3/h	Main motor KW	Vice motor KW	Dimension: L×D×H
LW250×1000	250	3600	1000	1813	1-3	7.5/11	4/5.5	2065×1050×800	1100
LW360×1200	360	3500	1200	2467	3-8	11/18.5	7.5/11	2600×1500×850	1900
LW360×1500	360	3500	1500	2062	3-8	11/18.5	7.5/11	2800×1400×850	2000
LW420×1750	420	3200	1750	2406	4-20	30/37	11/18.5	3120×1580×1050	3000
LW450×1600	450	3200	1600	2578	5-25	30/45	11/22	3780×1050×1180	3500
LW450×1800	450	3200	1800	2578	5-25	30/45	11/22	3985×1050×1180	3600
LW450×2000	450	3000	2000	2266	5─25	30/45	11/22	4320×1050×1180	3800
LW500×1800	500	3000	1800	2517	10-30	37/55	15/22	4200×1110×1200	4300
LW500×2100	500	3000	2100	2517	10-30	37/55	15/22	4500×1110×1200	4500
LW550×1800	550	3000	1800	2769	10-35	45/55	18.5/22	4380×1160×1230	4800
LW550×2200	550	2800	2200	2412	10-35	45/55	18.5/30	4780×1160×1230	5000
LW650×1750	650	2000	1750	1454	20-50	75/90	30/37	4576×1300×1250	6000
LW650×2000	650	2000	2000	1454	20-50	75/90	30/37	4900×1300×1250	6200
LW800×2000	800	1800	2000	1450	40-100	90/110	45/55	6052×1460×2100	10000
LW1000×2350	1000	1600	2350	1432	50-140	110/132	55/75	6850×1860×2300	12800