tungsten mining in gravity puction line

tungsten extraction, extraction of tungsten from scheelite, extraction of tungsten from wolframite

tungsten extraction, extraction of tungsten from scheelite, extraction of tungsten from wolframite

At present, the grade of raw tungsten ore in the world is decreasing year by year. There are less and less easy-to-mining wolframite, while refractory scheelite and wolframite-scheelite intergrowth ore gradually occupy the main position. Therefore, Xinhai Mining strengthens the research on tungsten extraction process, and customizes the ideal tungsten extraction equipment according to the different types of tungsten ore, strives to improve the tungsten extraction efficiency and reduce the production costs.

Xinhai uses the sodium sulfide, cyanide and chromate to inhibit the associated sulfide minerals, and adopts the sodium silicate, tannin, sodium polyphosphate, chromate to inhibit the gangue minerals. Then, using the sodium silicate or sodium carbonate to adjust the pH value of the pulp to 9.5-10, and 11-12 for cleaning stage.

Xinhai adopts sodium silicate heating method, which means adding a certain amount of sodium silicate to low-grade coarse concentrate, heating up, cooking, stirring, dehydration and slurry mixing, then concentrating repeatedly. Finally, the high-grade tungsten concentrate can be obtained.

That is, the jigging gross sand is produced when the qualified ore is sent to multi-stage jigging after the vibrating screen. The coarse-grained jig tailings are sent to grinding mill for re-grinding, and the fine-grained jig tailings enter into multi-stage shaking table after the classifier, then the shaking table gross sand is produced. The shaking table tailings are sent to the tailings pond, and the middlings are returned for regrinding and re-separating, and the gross sand of jig and shaking table is sent to concentrating stage.

Concentrating: Xinhai adopts flotation-gravity separation combined process or flotation-gravity separation-magnetic separation combined process, and recovers the associated elements in the concentrating stage.

Through the coarse and fine-grained table flotation (flotation -shaking table combined method) and flotation to remove the sulphide ore, the sulphide ore of table flotation and flotation merges into the sulfide ore flotation separation. And the wolframite after table flotation and flotation becomes the wolframite concentrate by the gravity separation process. If there are scheelite and cassiterite in the wolframite concentrate, gravity separation-flotation or gravity separation-flotation-magnetic separation combined process can be adopted to separate wolframite concentrate, scheelite concentrate and tin concentrate.

Fine sludge treatment: Xinhai usually carries out desulfurization first, and then adopts gravity separation, flotation, magnetic separation, electric separation or combined process to recycle the tungsten ore according to the properties of fine sludge, and utilize the associated metal minerals at the same time.

For the extraction of tungsten from wolframite-scheelite intergrowth ore, especially the fine-grained wolframite-scheelite intergrowth polymetallic ore, Xinhai usually adopts the bulk flotation process.

Bulk flotation of sulfide ore - bulk flotation of wolframite and scheelite - heating and separation of scheelite - strong magnetic separation of scheelite tailings - gravity separation of wolframite;

Before: The original plant adopted crushing pre-separation-gravity separation-concentrating process, which resulted in the loss of a large amount of fine-grained tungsten minerals, high mineral processing cost and poor mineral processing indexes.

After: After making the careful research on the ore properties and processing technology, Xinhai decided to optimize the wolframite process, add fine slime processing technology, and finally get the better mineral processing indexes.

After the modification, the recovery of fine-grained wolframite was strengthened obviously, and the influence of fine slime on the wolframite separation was reduced, which obviously improved the recovery indexes and the economic benefit of the plant.

Xinhai has make class B design qualification, and set up mine design institute and mineral processing research institute. More than 200 professionals provide the technical support service for 70 kinds of ore.

Depending on its professional mineral processing EPC+M+O service, Xinhai has got the EU certification, and ISO9001:2015 quality management system certification, who is classified as the assured brand with advanced products and standard quality!

Xinhai has multiple patents technologies, more than 500 mineral processing plants spread among China, Southeast Asia, South America, Africa, Iran, Russia, Mongolia, North Korea and other places, and Xinhai has established multiple overseas offices around the world.

tintungsten ore mining plant solution - jxsc machine

tintungsten ore mining plant solution - jxsc machine

Tungsten ore is a rock from which the element tungsten can be economically extracted. The ore minerals of tungsten include wolframite, scheelite, and ferberite. Tungsten is used for making many alloys.

Cassiterite is the best-known tin mineral. It has been used as the chief ore of tin from early history throughout the ages, and remains so even today. Some of the economical Cassiterite deposits exist in placer stream deposits where this very heavy mineral collects as rounded waterworn pebbles.

Feeding: according to the plant and minerals situation. miners can choose different feeding machines such as vibration feeder, hopper, belt feeder, or wheel loader and excavator. In order to remove big waste stones, Grizzly bar is always required to set before the feeding machine.

Washing: Trommel scrubber, screen machine, sand washing process are often used in the washing step. Trommel scrubber is highly recommended to use in breaking down sticky clay from raw material. If the raw ore is with little/light clay, trommel screen and spiral wash machine is fine.

Sizing: the sieving process is to classify the washed material into a different faction. Useless fraction would be gangue, the different useful fraction would be concentrated by a different machine. trommel screen, normal or high-frequency vibrating screen is frequently applied in the grading step.

Drying: Heavy mineral would be concentrated after the gravity method. the heavy minerals may have Tin, Tungsten, Coltan, Zircon, Gold. Magnetic separating is required to separate them. Drying Processing is needed before the process method for the Rock type.

Crushing: The crushing section is designed to remove the undersize between each crushing step to avoid an excess production of fines. Also, a Vibrating Screen is used ahead of the secondary crusher. The secondary crusher is operated in closed circuit with the vibrating screen to ensure a uniform product to the tin mining plant.

Concentration: The minus -1mm screen undersize is sized in a Hydraulic Classifier for most efficient tabling. Concentrating Tables with sand riffles handle the coarser sizes while the finer sizes are treated on decks riffled for finer sands. The rougher table concentrates are subsequently cleaned on two separate tables. In some cases, a portion of the rougher concentrate can be cut so as to yield some final concentrate not requiring retailing.

Drying: Heavy mineral would be concentrated after the gravity method. the heavy minerals may have Tin, Tungsten, Coltan, Zircon, Gold. Magnetic separating is required to separate them. Drying Processing is needed before dry type magnetic separator.

wolframite ore gravity production line-well-tech international mining equipment

wolframite ore gravity production line-well-tech international mining equipment

Wolframite consists of the quartz dyke type ores and veinlet tungsten ores. Dissemination size of ores is relatively coarse, so it is easy to separation. Our wolframite mineral processing is a combined separating technology which mainly use gravity separation. And four stages are involved in this process, roughing, gravity separation, cleaning, and slime treatment.

tin mining, tinning process, extraction of tin, tin mining process - xinhai

tin mining, tinning process, extraction of tin, tin mining process - xinhai

[Introduction]: The density of tin ore is larger than the paragenetic mineral, so the mining process of tin ore is gravity separation. However, all kinds of iron oxides exist in those ore, like magnetite, hematite, etc., which cannot be well separated by using gravity or flotation separation. Herein, magnetic separation and flotation separation will be used.

[Application]: Gravity separation is the traditional method for tungsten, tin and gold, especially placer gold and placer tin. It is also common in the application of rare metal placer ores(niobium, tantalum, titanium, zirconium and so on). It is also used for weak magnetic iron ore, manganese ore and chrome ore.

Put the 20~4mm ore into heavy medium cyclone to be selected. Then the ore will enter into the rod mill. After that, it will be preselected in jig. The tailings over 2mm will be abandoned, and the ore below 2mm will be put into shaking table.

After the bulk flotation, the concentrate will be fine grinded, then will be do the flotation separation of lead zinc ore. After that Lead antimony concentrates and zinc concentrates will be produced.

The tin pulp enter into 300mm hydrocyclone, then overflow to 125mm and 75mm hydrocyclone group to remove the fine mud. The sand setting will enter into the process of thickening, desulphurization by flotation, and then cassiterite flotation.

tungsten mines - an overview | sciencedirect topics

tungsten mines - an overview | sciencedirect topics

The collected data were the same as those used in the previous work (Nazari and Pacheco-Torgal, 2013). Three main series of geopolymers each made from a certain aluminosilicate source were considered in this study as in the previous work:

The first series of samples were the compressive specimens made from tungsten mine wastes. Tungsten mine waste mud, which was subjected to a thermal treatment, the fine aggregate which was crushed sand from the same mine, distilled water, the sodium hydroxide flakes, sodium silicate solution and calcium hydroxide were the materials used to produce geopolymeric compressive specimens using 505050mm3 cubic molds, according to ASTM C109. The complete preparation method of the considered geopolymers is given in Pacheco-Torgal et al. (2008).

Metakaolin-based geopolymers made from metakaolin, calcium hydroxide, sodium hydroxide, sodium silicate solution, superplasticizer, sand and distilled water were used to dissolve the sodium hydroxide flakes (Sarker et al., 2013). Alkali-activated mortars were a mixture of aggregates, metakaolin, calcium hydroxide and alkaline silicate solution were poured into 1604040mm3 cubic specimens according to EN 1015-11. The preparation method for compressive strength tests is presented in Pacheco-Torgal et al. (2011).

The third group of geopolymers made by tungsten waste mud consisted of aggregates, waste mud, calcium hydroxide, alkaline silicate solution and water in a similar way to the method described above for the data gathered from Pacheco-Torgal et al. (2008).

Mining is probably one of the most important global activities in the generation of high volume wastes. This type of wastes, called mine tailings, is usually inert from chemical and environmental points of view. In some specific cases, such as copper and tungsten mine tailings, due to their chemical and mineralogical composition, they are appropriate for using in alkali-activated binders.

Ahmari and Zhang have focused their research on copper mine tailing (MT) geopolymeric bricks. The procedure for producing the bricks simply includes mixing the tailings with an alkaline solution, forming the brick by compressing the mixture and curing at a slightly elevated temperature. Bricks met the ASTM requirements (Ahmari and Zhang, 2012). Durability and leaching behavior of geopolymeric bricks were studied. The results indicated that although there was a substantial strength loss after immersion in pH=4 and 7 solutions, the water absorption and weight loss were not significant. The leaching analyses showed that the heavy metals are effectively immobilized in the MT-based geopolymeric bricks, which was attributed to the incorporation of heavy metals in the geopolymeric network (Ahmari and Zhang, 2013a). The enhancement of copper mine tailings-based geopolymeric bricks with cement kiln dust (CKD) was studied (Ahmari and Zhang, 2013b). When CKD was used, an increase of unconfined compressive strength (UCS) and improvements in durability were produced. The effects of activator type/concentration and curing temperature on alkali-activated binder based on copper mine tailings were studied (Ahmari et al., 2012a). Some alkaline activators at different compositions, concentrations and curing temperatures were considered (see Table18.1). The results indicated that sodium hydroxide concentration and curing temperature are two important factors that affect the UCS and microstructural properties of the alkali-activated MT binder.

Zhang et al. (2011) studied the viability of geopolymerization of copper mine tailings adding different amounts of fly ash in order to decrease the high Si/Al ratio of the mine tailings. The results showed that the Si/Al ratio and the alkalinity have very important effects on the mechanical and microstructural properties of the mine tailings-based geopolymers.

Pacheco-Torgal et al. (2008c, 2008d, 2008e, 2008f, 2009, 2010) have carried out exhaustive studies on tungsten mine waste. Tungsten mine waste mud (TMWM) geopolymeric binder is a new cementitious material with a very high early age strength, low water absorption and very good adhesion to ordinary Portland cement (OPC) concrete (Pacheco-Torgal et al., 2008c, 2008f). It is obtained from dehydroxylated mine waste powder mixed with calcium hydroxide and activated with NaOH and waterglass solutions. The results showed that techniques and procedures for assessing OPC fresh mixtures are not recommended to evaluate TMWM binders. Unrestrained shrinkage of TMWM binders is lower than observed for OPC binders, being even lower than some traditional alkali-activated binders (Pacheco-Torgal et al., 2008d). The effect of the aggregate/binder ratio, the aggregate dimension and aggregate type (schist, granite and limestone) in the microstructure and mechanical behavior of tungsten mine waste geopolymeric pastes and mortars were investigated (see Figure18.4). In contrast with the porous typical interfacial transition zone of Portland cement mixtures, a dense and a uniform interfacial transition zone was detected in tungsten mine waste geopolymeric-based binders (Pacheco-Torgal et al., 2008e).

Figure18.4. SEM micrograph of interfacial transition zone in tungsten mine waste geopolymeric mortars made with granitic coarse aggregates. Area D presents a sodium content of 3.4% (%Na2O) obtained by EDS.

Research on geopolymeric mine waste mud (GMWM) binders hydration products has been carried out. Results showed that a new crystalline phase, phlogopite with a trioctahedral layered structure, was formed as a result of the geopolymerization process (Pacheco-Torgal et al., 2009).

Durability and environmental performance of TMWM mortars were carried out. This study showed that TMWM binders have higher acid and abrasion resistance than OPC-based concrete mixtures. The environmental assessment of the TMWM binders showed that it can be considered inert from an environmental point of view and it could be used as a construction material (Pacheco-Torgal et al., 2010).

Silva et al. (2012) studied the behavior of alkali-activated TMWM after immersion in water. A mixture of waterglass and sodium hydroxide as an activating solution was used. Additional specimens with high water content (10% in relation to mass precursor) were cured for several weeks at 20C and 40% RH, 80C and 130C dry conditions. Afterwards, specimens were immersed in water for different periods. Alkali-activated specimens cured at room conditions (20C 40% RH) partially disintegrated when immersed in water. Disintegration of specimens was due to deficient geopolymeric reaction (partial alkali-activation reaction), which could have been caused by an insufficient concentration of NaOH solution.

Castro-Gomes et al. (2012) have developed new geopolymer-based composite materials, obtained from non-contaminated waste-rock tailings. These materials could have interesting properties for technical-artistic value added applications, such as conservation, restoration and/or rehabilitation of historic monuments, sculptures, decorative and architectural interventions, or simply as materials for building coatings.

Komnitsas and Zaharaki (2007) have published an interesting paper about minerals and geopolymerization. The paper presented a brief history and review of geopolymer technology, summarized and critically analyzed the most important research findings over the last 25years. Finally, the paper proposed further research and development topics and suggested steps forward (see Figure18.5) to improve the potential of geopolymerization focusing on the utilization of mining and metallurgical wastes and by-products, the synthesis properties and the stabilization of hazardous wastes.

MT are waste materials generated from mineral processing operations. MT are fine particles and mainly constitute silica and alumina minerals and thus are suitable for geopolymerization. Their phase and chemical compositions are variable and dependent on the properties of the mother rock and the mineral processing operations they have undergone. In general, MT are mainly crystalline material and thus it is relatively difficult to produce geopolymer binder from them. Pacheco-Torgal et al. (2008, 2010) and Pacheco-Torgal and Jalali (2010) conducted an extensive study on production of geopolymer concrete from tungsten mine waste. In order to improve the reactivity of tungsten mine waste, they dehydroxylated the mine waste by heating at 960C during which the -OH- group is liberated from the chemical bonds and the molecular structure is transformed into a disordered one.

Ahmari and Zhang (2012, 2013a, 2013b) investigated the production of GMU from copper MT. They prepared small size cylindrical specimens of MT-based geopolymer brick activated by NaOH and cured at 60120C. The specimens were formed at varying pressures from 0 to 25MPa and initial moisture contents from 10 to 18%. They reported 90C as the optimum temperature for NaOH-activated MT and initial moisture content and forming pressure as the most important factors that affect the physical and mechanical properties of the MT-based GMU. The produced MT-based GMU produced met or exceeded the ASTM criteria for different applications of GMU. However, Ahmari and Zhang (2013b) reported substantial strength loss of MT-based GMU in water and nitric acid at pH4. The durability of the MT-based GMU was enhanced by adding a small amount of cement kiln dust (CKD) (Ahmari and Zhang, 2013a). The physical and mechanical properties of MT-based GMU can also be enhanced by adding FS. Addition of other types of waste material to MT creates a hybrid geopolymer system, which can effectively improve the physical and mechanical properties and durability of MT-based GMU.

Dehydroxylation involves the heating process through which the hydroxyl group (OH) is released by forming a water molecule (Frost & Vassallo, 1996). The generally accepted mechanism of dehydroxylation of kaolinite is the interaction between two liberated hydroxyl as below:

The process requires proton delocalization at specific hydroxyl sites. The consequence of the release of structural water through dehydroxylation is distortion and buckling of polymeric structure of aluminosilicates, resulting in disordered structure (Sperinck et al., 2011).

Pacheco-Torgal & Jalali (2010) studied dehydroxylation of tungsten mine waste with and without adding sodium carbonate. They heated the mine waste and cooled it down rapidly to assure that the crystalline structure is transformed to an amorphous one. The reason for the addition of sodium carbonate was to reach the criteria Na2O/SiO2>0.2 given by Davidovits (Davidovits, 1999). The study indicated that with no addition of sodium carbonate, dehydroxylation at 960C resulted in the highest compressive strength of the geopolymer product. The addition of sodium carbonate did not lead to an optimal temperature (dehydroxylation state) although the compressive strength of sodium carbonate-added specimens was higher.

The dehydroxylated tungsten MT-based geopolymer concrete exhibited good physical and mechanical properties (Pacheco-Torgal etal., 2008a). The water absorption by immersion (WAI) after 24h immersion in water was on average below 3.4%. The capillarity water absorption coefficient (CWAC) was below 0.015g/cm2. Comparison between the CWAC of the geopolymer concrete and that of the aggregates indicated that the measured values (0.00070.005g/cm2) primarily represent the water absorption of the geopolymer paste. The measured static elastic modulus (29.734.9GPa) showed dependence on the type and size of the aggregates used. The compressive strength after 50days of curing was reported to increase to about 40MPa for hardened geopolymer paste and more than 90MPa for geopolymer concrete. This indicates the effectiveness of dehydroxylation for pretreatment of MT. However, since the main goal for using MT-based geopolymer is to develop sustainable materials and considering the energy intensiveness of the dehydroxylation process, commercialization of this process is still questionable.

Unrestrained shrinkage (US) for mine waste geopolymeric binders is shown in Fig. 13.6. The mass ratio of water/dry solid binder content was 3.6% in most of the samples, except for samples with an aggregate/binder mass ratio of 1.5 or 1.7 in those cases, the extra water percentages were respectively 7 and 10%. TMWM binders using schist (SC) fine aggregates with an aggregate/binder ratio of 1.5 was named SC AG/B 1.5. Similarly when limestone (LS) or granite (GR) aggregates were used were named respectively LS AG/B 1.5 and GR AG/B 1.5. TMWM mixtures made with 2% superplasticizer by mass of binder lime and mine waste mud, were named respectively SC/SP, GR/SP and LS/SP. Unrestrained shrinkage used prismatic specimens measuring 40 40 160mm3 and was determined according to Portuguese Standard LNEC E398-1993. Unrestrained shrinkage readings were performed every hour in the first 10h, every 3h in the next 6days and twice a day in the remaining days.

Unfortunately, as the apparatus only measures shrinkage 24hours after the mixtures were cast, it misses an important part of US deformation, that may take placed between the time when setting occurs until the specimens were removed from the moulds and place in the device. That hypothesis can only be confirmed using a test device that could measure US deformation since the beginning of setting, something that cannot be done with the Vicat penetration test which is currently used for oPC technology, where the shrinkage deformation in the first 24h is disregarded (Aitcin, 2001). The US data shows a different behaviour for mine waste mortars with an aggregate/binder mass ratio between 1.0 and 1.5 and the ones with the equivalent 0.5, which have higher shrinkage than the pastes. As the aggregates percentage used in the mortars is much lower than for concretes, i.e mortar aggregate/binder mass ratio is below 2.0 versus between 4 and 5 for concrete, it follows that aggregates act as a set of inclusions trapped in a continuous paste matrix and do not form a rigid skeleton which help to diminish US deformation (Aitcin, 2001; Tazawa and Myazawa, 1995). So increasing aggregate content in terms of aggregate/binder mass ratio from 0.5 to 1.5 is not enough to achieve a US reduction. Besides the volume change associated to the shrinkage behaviour is also dependent on the mass of specimens, i.e the US will be higher for lower mass and higher porosity.

Tungsten minerals that occur in sufficient abundance to be of economic significance and can be used in the production of APT are divided into two groups: scheelite ores and the wolframite ores (Lassner & Schubert, 1999).

The mineral scheelite (calcium tungstate, CaWO4) is normally found in quartz veins and in contact with scarn ores of complex mineralogical composition (Lassner & Schubert, 1999; Singh & Miller, 1998; Singh, Miller, & Wolfe, 1999, 2000). These scarn minerals include garnets, pyroxene, and amphibole, and other minerals such as calcite, apatite, and quartz. Figure 3 depicts a picture of a scheelite tungsten mine. Scheelite ores can be classified into five different categories: (1) simple scheelite ore, (2) scheelite-sulfides ore, (3) scheelite-cassiterite ore, (4) scheelite-calcite-apatite ore, and (5) scheelite-powellite ore.

From an ore, scheelite is typically concentrated via a flotation process (Agar, 1984; Lassner & Schubert, 1999; Vedova & Grauerholz, 1977; Zajic & Kosaric, 1977). In a typical scheelite ore concentration process (Figure 5), the ore (containing 0.4-0.6 %W) from the mine is brought to the plant and fed to the grinders to grind below 200 mesh. Ground ore is slurried in water and the slurried ore is cycloned. Overflow from the cyclone goes for talc flotation; concentrates from talc flotation cells go to tailings (reject); and tail from the cell is screened: oversized concentrates go to tailings (reject) and undersized concentrates go to low-grade ore thickeners for reclaim as low-grade ore. The underflow from the cyclone is screened and the oversized concentrates are returned for regrinding. The undersized concentrate goes to high-grade ore feed to the thickener. The ground material goes back to cyclone. The thickened mud is conditioned for sulfide flotation. Concentrate from the flotation cell (mainly sulfides) goes to the tailings (reject). The tailing of sulfide flotation cells goes to the tables (rougher and cleaner) for high-grade ore concentrate separation. The ore portion collected at the corners of the high-grade ore separation tables is the low-grade ore feed and goes to the thickeners.

High-grade ore concentrate, collected from the tables, goes to the roaster and is roasted at about 540C to remove organics. The roasted high-grade ore goes to magnetic separator for final sulfide cleaning. Clean ore is bagged and shipped. The magnetically separated material goes for another magnetic separation. Rejects from this magnetic separator go back to the cleaner tables.

In high-grade ore separation tables, rougher tables pull (concentrate) scheelite, which then goes to the cleaner tables. Tailings from the rougher go for scheelite scavenging. The scavenged scheelite goes back to the rougher tables. Scheelite from the cleaner tables goes to high-grade ore collection. All the tailings from the rougher and cleaner tables are the feed for low-grade ore and go to low-grade ore thickeners. Coarser material from the high-grade rougher tables goes for cyclone separation. Underflow from the cyclone goes for ball milling and secondary sulfide flotation and back to high-grade ore tables; overflow goes to thickener for low-grade ore feed. Figure 5 presents the general flow diagram of the scheelite concentration process.

The wolframite ores consist of three minerals: ferberite, wolframite, and hubnerite. The iron-rich tungstate (FeWO4; WO3 content 76.3%) is ferberite, the manganese-rich tungstate (MnWO4; WO3 content 76.6%) is hubnerite, and the iron-manganese-mixed tungstate ((Fe,Mn)WO4; WO3 content 76.5%) is wolframite. Wolframite contains between 20% and 80% each of FeWO4 and MnWO4 in their pure form. Table 3 presents the composition of three wolframite ore concentrates. Concentration of wolframite from its ores is typically carried out by gravity and magnetic methods, as wolframite occurs mainly in vein-type deposits whose mineralization is much coarser than most of the scheelite ores (Lassner & Schubert, 1999). Figure 6 depicts wolframite ore in a tungsten mine.

Pno: 203 AAB are most commonly based on blast furnace slag, metakaolin (calcined clays), and/or coal fly ash as prime materials. Other industrial waste and natural materials have been used to a limited extent. However, it is worth mentioning such materials, as their use represents alternative routes for the development of AAB. Steel (ladle) slag, phosphorus slag, ferronickel slag, non-ferrous metallurgy slags, red mud, waste ceramic, tungsten mine waste, copper mine tailings, fluid catalytic cracking catalyst residue, air pollution control residue glass, cement-rich fraction of construction and demolition waste, municipal solid waste incineration ash, palm oil fuel ash, rice husk and bark ash, volcanic ash, kaolinitic clay, natural zeolites, and natural pozzolans, have been used among others. The list of potential prime materials is growing as the interest in the development of more green and sustainable materials in the environmentally conscious age also grows.

Combined mechanical and chemical (alkali) activation provides a plausible solution for the use of lower quality prime materials in terms of their homogeneity, particle size, and reactivity. The quest for an inexpensive and abundant alkali activator is still in progress. Sodium aluminate, especially as an industrial waste source, showed respectable potential in the process of alkali activation. Little attention was paid to the mixing procedures during AAB preparation, as they may significantly affect the mechanical properties of AAB. More attention should be paid to such alternatives in the future.

Excess of water needed for the proper workability achievement still remains a limiting factor. Standard water reducing admixtures developed for the Portland cement systems do not work properly under high alkaline conditions present during the alkali activation process. The development of such admixtures would provide significant impact to the mechanical properties and durability improvement, and consequently to wider structural and non-structural applications of AAB.

Despite being the basic mechanical properties of AAB, comparing the results of mechanical strength and modulus of elasticity is not a simple task due to numerous differences in experimental conditions. Lack of standard testing procedures developed for AAB systems is widely recognized. Very high compressive strength of AAB can be obtained, even at room temperature. The flexural/compressive strength ratio of AAB is equal or better than its OPC counterpart. However, high sensitivity of AAB to environmental conditions, especially to relative humidity at early age, still exists. Therefore, appropriate curing to full maturity of AAB is one of the most important factors which should be controlled. Unconventional curing by ultrasound or microwaves was also recognized as a plausible improvement. Other routes for accelerated curing, especially those based on low energy consumption, should also be explored.

The majority of the results of mechanical properties presented here have been achieved more by trial and error than by an in-depth understanding of what is happening at the micro- or nanoscale. Nanoindentation of the constituent phases of AAB provides new means of correlating mechanical properties at the nanoscale to macroscale properties of AAB and possible applications.

Generally AAB, like cement-based systems, exhibit relatively poor tensile and flexural properties. The incorporation of different types of inorganic or organic fibers (steel, E-glass, wool, PVA, PVC, carbon) increases flexural strength, splitting tensile strength, and ductility of AAB. It also changes fracture behavior from brittle to a more ductile pattern. The addition of fibers represents the major route for improvement of AAB elastic properties.

High-temperature heat treatment of carbon fiber reinforced geopolymer composites produced ceramic material with outstanding mechanical properties, i.e. flexural strength of ~234MPa and Youngs modulus of ~64GPa. Multiwalled carbon nanotube reinforced geopolymers are proposed as self-sensing materials capable of detecting their own structural damage. Such new types of materials based on AAB can contribute to the expansion of AAB fields of application.

With this current study and the few previous LCA studies made on geopolymer concrete, it seems clear that particular attention needs to be paid to the definition of the functional unit, the data quality and the impacts considered, in order to make an accurate environmental assessment of AACC.

This study highlights that focusing on a functional unit of 1m3 of concrete with a given compressive strength in the solid state is not enough to compare alkali-activated concrete to standard concrete. We show that the volume of the paste must also be the same. It does not drastically change the results, but some particular mix comparisons can appear to be much less or much more interesting than initially suggested. Another aspect that can influence the outcome of an LCA is the system boundary. Yang et al. (2013) provided a complete assessment considering the emissions of the materials, transport from cradle to the building site, production and curing phases. In other cases, studies have been reduced to cradle to gate. In some specific case, especially when dealing with waste valorization, a larger system boundary can be needed as one of the advantages of AAC is that inorganic waste, which would otherwise have to be landfilled, can be used. For example, while magnesium iron slags (Zosin et al., 1998), ferronickel slags (Komnitsas et al., 2007) or tungsten mine waste mud (Pacheco-Torgal et al., 2007) are of little or no benefit in blended cement technology, they can be used successfully as geopolymeric binders.

The common result of all studies is that the sodium silicate solution is the greatest contributor to the CO2 emissions, representing nearly half of the total emissions, while the clinker represents two-thirds of the impact for standard concrete (Figure25.4). Furthermore, there is a consensus on the fact that the data on sodium silicate are hard to estimate. Turner and Collins (2013) found that manufacturers would not disclose the information on energy usage and emissions from their processes. Thus, most of the studies calculate the impact based on the comprehensive analysis summarized in a paper published by Fawer et al. (1999), which is based on the production year of 1995, 20years ago. The process of production of sodium silicate must have improved since that time and the impacts are most probably reduced. The data on metakaolin also needs to be estimated, but it has less impact on the final result. The update on the sodium silicate data has the potential to change the outcome of the LCA of AACC.

In most LCA of AACC, the only impact category is the equivalent CO2 emissions. Comparing AACC and OPC concrete only on the basis of the equivalent carbon emission does not provide a representative picture of the global impacts. Figure25.5 shows the environmental impact of geopolymers in the ten classic impact categories used in LCA, where 100% corresponds to the impact of OPC concrete. FA and GBFS geopolymers may be beneficial in term of GWP, but the impacts in the other categories are clearly superior. It is, however, not easy with this calculation to know if the environmental impact for the other categories is of significant importance, even if it is higher than OPC concrete. For instance, we know that cement production represents more than 5% of the global anthropogenic CO2 emissions, but what is the contribution of cement production to the acidification of the freshwater ecotoxocity? If we consider GWP as an important impact, we then need to know the impact in other categories relative to GWP.

Figure25.5. Eco-profile of different geopolymer concrete types compared to OPC-based concretes. The pure OPC concrete binder is made exclusively with CEM I, whereas current concrete binder is on average prepared with 70% CEM I and 30% mineral addition.

One method used in LCA is normalization. In this method, the impacts for the different categories are normalized by dividing them by the yearly impact of an average citizen, here a European citizen. The results of this normalization are presented in Figure25.6. For the sake of clarity, the normalized impacts are then all compared to the GWP. 100% in one impact category means, then, that the contribution of the cement production to this category is almost equal to its contribution to the GWP. Results show that geopolymers have greater impacts in the categories of abiotic depletion, freshwater toxicity and marine toxicity. So if CO2 emissions is an important issue, these three categories of impact are even more sensitive and it becomes relevant to include them in the comparative assessment between OPC and geopolymer. It also shows that promoting geopolymers can induce a risk of pollution transfer. Since most of the impacts of the geopolymer are from the sodium silicate solution, revising the data on the sodium silicate is a priority in order to create a clear view on the life cycle assessment of alkali-activated cements and concretes.

Tungsten mine tailings in the present experiment were from Jiangxi of China, and it was subject to a thermal treatment at 900C during 2h, in order to achieve the dehydroxylated state [15]. The chemical compositions of the heat-treated tailings were determined by X-ray fluorescence analysis (ZSX Primus II, 50kV-60mA) and the result was shown in Table 2. The raw materials of preparing ceramic substrate were heat-treated tungsten mine tailings, aluminum oxide (Al2O3) (99.9%) and magnesium oxide (MgO) (99.9%). The contents are showed in Table 3. The granular size of raw materials was 110m, and well mixed.

The samples were prepared by a laboratory uniaxial dry-pressing into disk shapes with a diameter of 50mm, thickness of 10mm, using a pressure of 30MPa. The obtained green specimens were then sintered in an electric laboratory furnace with a heating rate of 3C/min. They were firstly treated at 450C for 1h in order to remove the residue water and protect the samples from cracking caused by the uneven thermal distribution. Subsequently, each sintering process was carried out in duplicate at different maximum temperatures, at 1000C, 1050C, 1100C, 1150C, 1200C and 1250C, respectively, and holding for 2h, to evaluate the effect of this parameter on the characteristics of the ceramic substrates. Natural convection inside the furnace was used for cooling to room temperature. The samples of ceramic substrate were obtained.

Mine tailings (MT) are a residual material from mine operations and are mainly composed of finely-ground sand to silt-sized rock particles, water, and processing reagents used to extract valuable minerals from the ore (Natural Resources [59]). With the number of minerals extracted and processed each year around the world by the mining industry, the volume of MT is enormous, e.g. worldwide MT generation is estimated to be >7 billion tons per year. Therefore, this matter should be of concern in metal producer countries since the proper disposal of MT requires not only a lot of lands but can also constitute a hazardous environmental problem as dangerous heavy metals can reach aquatic ecosystems [84]. As MT disposal is potentially toxic in some cases and could involve an elevated cost to satisfy environmental regulations, its potential use as raw material for geopolymerisation has generated great interest.

As shown in Table 5, copper and tungsten MT have already been widely studied as starting materials for geopolymer production. Pacheco-Torgal et al. [63] evaluated the use of tungsten MT that was composed mainly by SiO2, Al2O3, Fe2O3 and K2O. They used a mixture of NaOH 24M and sodium silicate (Ms=1.34) as the activating solution and cured their samples at room temperature, the geopolymers formed showed a 56-day compressive strength of 45.5MPa. The same curing conditions were employed by Pacheco-Torgal & Jalali [65] to obtain a tungsten MT geopolymer paste with a 28-day compressive strength of 40MPa using an alkaline solution with a Na2SiO3/NaOH mass ratio of 2.5. On the other hand, Silva et al. [91] employed a curing process consisting of two stages to produce a binder with compressive strength up to 24MPa. In the first stage, specimens were left at room temperature and then were heated at 80C in the second stage. Regarding the use of copper MT, Ahmari et al. [1,2] studied the effect of curing temperatures and alkaline solutions in the activation and resulting compressive strength of geopolymers. The chemical composition of cooper MT used by Ahmari et al. [1,2] was mainly SiO2 and Al2O3 with a substantial presence of CaO and Fe2O3. They found that an alkaline solution of sodium aluminate and 10M NaOH at a mass ratio of 1.25 and a curing temperature of 90C for 7days produced a cooper MT-based geopolymer with a compressive strength of 17MPa. Besides copper and tungsten MT, iron MT has also been used as raw material for geopolymers production. For instance, Kuranchie et al. [50] developed iron MT geopolymers with a 7-day compressive strength of 50MPa and water absorption of 9% meeting ASTM requirements for the specification of bricks. The formulation of this geopolymer matrix consisted of an activator content of 31% and curing conditions of 7days at 80C. Another approach that has been gaining attention is mixing MT with other alumino-silicate materials to obtain a blended raw material with enhanced reactivity. In this line, Zhang et al. [115] produced hybrid geopolymers made from mixtures of fly ash and cooper MT, which resulted in compressive strengths in the range of 3MPa (pure copper MT-based geopolymer) to 14MPa (75% of flay ash replacement) at 7days of age. Kiventer et al. [43] investigated the alkaline activation of a mix of gold MT and GGBFS. They found that GGBFS has great potential as a co-binder of gold MT since a replacement of this material by 25% (wt%) of GGBFS increased the compressive strength from 3MPa (pure gold MT-based geopolymer) to 25MPa. Another example of hybrid MT geopolymer is the one reported by Wei et al. [102]. The main objective of their work was to explore the mechanical activation (MA) of vanadium MT. However, they used a constant metakaolin replacement of 50% (wt%) during all the investigation to provide additional reactive Al to the mix. They pointed out that milling raw MT modify the physicochemical characteristics of the vanadium MT as particle size and amorphous content leading to a better reactivity of the raw material [102]. The alkaline activation of the mix of the MA vanadium MT and metakaolin in a weight ratio of 1:1 produced a geopolymer matrix with 14-day compressive strength of 25MPa, 190% higher than the strength obtained by geopolymer produced with raw vanadium MT.

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