WO2011141297A1

WO2011141297A1 - Lithium-bearing slag as aggregate in concrete

Info

Publication number: WO2011141297A1
Application number: PCT/EP2011/056750
Authority: WO
Inventors: Begum Yaziciogly; Jan Tytgat
Original assignee: Umicore
Priority date: 2010-05-12
Filing date: 2011-04-28
Publication date: 2011-11-17

Abstract

This invention concerns the use of lithium-bearing additives in concrete or mortar. Such additives are obtainable by a high temperature process wherein lithium-bearing materials such as scrapped lithium-ion batteries are smelted. More particularly, lithium-bearing metallurgical slag is presented as an additive for reducing the undesired ASR (alkali-silica reaction) in concrete or mortar. The lithium-bearing metallurgical slag substitutes fine or coarse aggregate, and appears as effective in mitigating the ASR as the expensive lithium salts normally needed.

Description

Lithium-bearing slag as aggregate in concrete

This invention concerns the use of lithium-bearing additives in concrete or mortar. It is known that lithium can mitigate the detrimental effects of alkali excesses in concrete by minimizing the AAR (alkali- aggregate reaction), e.g. from "Alkali-aggregate reaction suppressed by chemical admixtures at 80 °C", Xiangyin M., Tongshun J., Construction and Building Materials (2005). This AAR is a reaction in concrete between the alkali hydroxides, which originate mainly from the Portland cement, and certain types of aggregate. Two types of AAR are recognized, namely the ASR (alkali- silica reaction) and the ACR (alkali-carbonate reaction). As the names imply, these types of reaction differ in that they involve reactions with either siliceous or carbonate phases in the aggregates. The ASR is far more widespread than the ACR.

The ASR is a chemical reaction between the alkalis in the concrete and certain aggregates comprising siliceous rocks and minerals, such as opal, chert, microcrystalline quartz, and acidic volcanic glass ("reactive aggregates"). This reaction, and the ensuing generation of alkali-silica gel, can lead to the abnormal expansion of concrete. This results in crack formation, and in the deterioration of the mechanical properties.

Portland cement is the main source of alkalis, but the aggregates and other chemical admixtures can also contribute. The amount of alkalis is expressed as Na₂0 equivalents.

The occurrence of the ASR is in particular exacerbated when using cement combining high amounts of alkali with the presence of reactive aggregates.

As mentioned above, measures to mitigate the ASR are, apart from using non-reactive aggregates and cement with a low alkali content, the admixture of lithium compounds. Lithium salts such as L1NO₃ are commonly used. A molar ratio of Li : (Na + K) of between 0.6 and 0.9 has been found to suppress expansion adequately. See "US Department of Transport - Guidelines for the Using Lithium to Control ASR in New and Existing Concrete Structures"; Chapter 5. The mechanisms by which lithium reduces expansion are however not well understood.

These measures all have an undesired impact on the costs. The added lithium salts can in particular represent a significant fraction of the total costs of concrete. This is illustrated in "Economics of Lithium Technology for ASR Control vs. Alternatives", Manissero C, Concrete in Focus, Concrete InFocus Magazine, (Fall 2006).

EP1589121(A) discloses a lithium battery recycling process using a shaft furnace, producing a lithium-bearing slag that is used as a gravel substitute in concrete. The environmental stability of concrete containing 30% of such slag is tested by percolating acidified water through the comminuted concrete. However, the use of Li-bearing slag as substitute for fine aggregate such as sand is not shown, and the reduction of the ASR in not disclosed.

An article by Z. Ruopeng et al., "Study on high strength and high fluidity concrete with lithium lag and silica fume", Industrial Construction (2004), Vol. 34, No. 12, pp. 61-62, teaches that up to 15% by weight of lithium slag can advantageously be added to concrete. The said lithium slag is however not characterized, neither in terms of its lithium content, nor in terms of is particle size distribution. There is no teaching as to any effect on the ASR. The present invention aims at providing a cheap and environmentally friendly source of lithium, which is compatible with the manufacture of concrete, and for which the benefits of lithium with respect to the suppression of the undesired ASR can be demonstrated.

To this end, a process is divulged for the production of lithium-bearing concrete, comprising the steps of: reduction smelting of lithium-bearing metal scrap, thereby obtaining a metallic phase and a lithium-rich slag; separating the slag from the metallic phases; cooling the slag, thereby solidifying it; and admixing the solid slag as aggregate in the preparation of concrete or mortar. Lithium batteries or their scrap, e.g. after shredding, are a preferred and valuable source of lithium-bearing metal scrap; primary as well as rechargeable batteries can be considered. Such batteries moreover contain transition metals such as cobalt, nickel, manganese, copper and iron, which will form a metallic phase during the reduction smelting step. The slag is preferably used to substitute fine aggregate, i.e. particles of less than 4 mm. Size reduction can be obtained by atomization or comminution. The latter is advantageously performed after granulating the molten slag in a liquid medium such as water. A particle size distribution having a dc>o of less than 4 mm, or even of less than 1 mm, is preferred. The finer particles ensure a better availability of the enclosed lithium and are thus more effective in ASR mitigation.

The slag should contain a sufficient amount of lithium in view of the amount of alkali in the other components of the mortar or concrete. To ensure a complete inertization in view of the ASR, at least about 0.6 mol of lithium per mol of alkali in the concrete is needed. Higher ratios, such as more than 1 , or even more than 2 mol per mol, are preferred, in particular when the amount of fines in the aggregate is low.

The above compositions can be obtained by replacing all or part of the aggregates by lithium-bearing slag particles. The minimum amount to be replaced can easily be calculated from the total alkali content of the concrete and the lithium content of the slag.

In practice, and in particular when lithium batteries are recycled, a slag with at least 1 wt.% of Li₂0, preferably at least 2 wt.%, is preferred. The smelting process is indeed most suitable for the production of such a slag. Another embodiment of the developed solution concerns concrete or mortar containing a metallurgical slag as an admixed aggregate, characterized in that the slag contains at least 2 wt.% of Li₂0. Replacing aggregates in concrete by metallurgical slag brings clear economical and environmental advantages. The extraction of natural aggregates is indeed avoided, as is the corresponding environmental burden. The slag, which may otherwise have to be dumped, gets a dedicated and useful purpose. It moreover appears that the use of lithium-bearing slag has a positive impact, mitigating the ASR issues in mortar and concrete. The separate addition of specific lithium salts can therefore be avoided, again with a positive economical and environmental impact as the winning and refining of the corresponding amounts of lithium becomes superfluous. When ion-batteries are recycled as lithium source, the other valuable metals such as cobalt, nickel, copper and even iron, are all efficiently recovered in a separate metallic phase. This phase can be further refined to pure metals using known processes.

For the determination of the impact on the ASR, accelerated expansion tests are performed according to CUR Recommendation 89:2002, "Ultra-accelerated mortar bar expansion test (UAMBT)", Appendix E. This test is further referred to as "standard", unless otherwise specified.

According to this standard, mortar bars are prepared. Mortar, compared to concrete, is prepared using exclusively fine aggregates instead of a mixture of fine (< 4 mm) and coarse (> 4 mm) particles. Mortar is indeed more suitable than concrete for accelerated, lab-scale testing. The expansion behaviour of mortar is considered representative for the behaviour of concrete made up from ingredients having the same chemical composition.

To prepare a mortar bar, CEM I 42.5R Portland cement with an equivalent Na₂0 content of 0.73% is selected. Additional NaOH is added to reach 1% of Na₂0 equivalent, as required by the standard. To it are added demineralised water, a first aggregate (#1) consisting of Tournai limestone with an equivalent Na₂0 content of 0.02%, and a second aggregate (#2) being, according to the invention, a lithium-bearing slag. The quantities are shown in Table 1. The details of the preparation are according to NEN-EN 196-1.

Table 1 : Composition of the mortar bars

The fresh mortar is moulded and left to dry in a climate chamber at 20 C and 90% RH for 24 h, after which the test pieces are de-moulded. Following this, the initial length Li of the bars is measured.

The bars are stored in a container with demineralised water. The container with the bars is placed in an oven at 80 C for 24 h, after which the length Lo is measured.

The bars are then transferred to a container containing 1 M NaOH solution, and are placed in an oven at 80 °C for 14 or 28 days. The length is then again measured as L_n (n being 14 or 28).

The relative expansion is calculated as e_n = 100 . ( L_n - L₀ ) / Li. If the relative expansion after 14 days is lower than 0.1%, the materials are considered as non ASR-reactive, whereas the materials that show a greater expansion are considered as reactive.

In some studies, expansion measurements after 28 days are said to be more representative of the long-term expansion. Therefore, both e₁₄ and e₂8 are reported here.

Example 1: Process for the preparation of a lithium-rich slag

A lithium-ion battery based charge shown in Table 2 is smelted according to the invention in a furnace with a diameter of 1.5 m lined with chrome-magnesia bricks, the lining having a thickness of 300 mm.

The feed comprises 60.95% by weight of lithium- ion batteries and scrap. A bath temperature of 1450 °C is obtained without additional cokes or gas. Oxygen is blown through a submerged burner at a rate of 285 Nm3/h. This burner is used as a tuyere for oxygen only, i.e. without simultaneous injection of any kind of fuel. Fuel, such as methane, is only used for the preparation of a starting bath of molten slag, and during tapping.

As an essential part of the metallurgical charge, batteries and battery packs weighing up to 50 kg are dropped into the molten bath from a height of 8 m. The furnace is operated in a mode allowing for freeze lining. Freeze lining is established by applying intensive cooling in of the slag zone, using water-cooled copper blocks according to known ways. Essentially no degradation of the furnace lining over time is observed.

Excellent recovery of the metals Co, Ni, Cu and Fe is observed with no added energy requirements. About 86% of the lithium is recovered in a slag containing about 3.9% by weight of lithium, corresponding to 8.4% Li₂0. This slag is separated from the metallic alloy phase by tapping, and cooled to solidification. The slag is then comminuted to the required particle size for use as Aggregate #2 according to Table 1 here above. Other slag compositions can easily be obtained by varying the relative amount of lithium-bearing material in the feed, or by choosing materials with a different lithium content. Table 2: Preparation of a lithium slag in a process for recycling lithium- ion batteries

Comparative Example 2: ASR expansion of mortar prepared according to a reference mixture

A mortar bar is prepared and tested according to the above-described standard. For Aggregate #2, use is made of a classical reference material, being Normensand, which has an equivalent Na₂0 content of 0.40%. This reference mixture contains no lithium.

Figure 1 shows the expansion in function of time: 0.18% after 14 days, and 0.27% after 28 days. This mixture is thus to be considered as ASR reactive, and therefore subject to ASR degradation.

Comparative Example 3: ASR expansion of mortar prepared with iron blast furnace slag

This example is similar to Example 2, but using a classical blast furnace slag as Aggregate #2. This slag contains a negligible amount of lithium, about 0.02%> expressed as Li₂0. Its Na₂0 equivalent amounts to 0.40%. It can be calculated that the lithium concentration in the mortar is 0.006%, corresponding to a Li : (Na + K) molar ratio of 0.03 only.

Table 3: Composition of blast furnace slag

Figure 2 shows the expansion in function of time: 0.12% after 14 days, and 0.19% after 28 days. This mixture is thus to be considered as ASR reactive, and therefore subject to ASR degradation. This poor result is to be expected in view of the use of reactive aggregates and a the very low Li : (Na + K) ratio. Example 4: ASR expansion of mortar prepared with lithium-bearing slag (2.57%)

This example is similar to Example 2, but using a slag prepared according to a process similar to Example 1 for use as Aggregate #2. This slag contains a low yet significant amount of lithium, about 2.57% expressed as Li₂0. Its Na₂0 equivalent amounts to 0.29%>. It can be calculated that the lithium concentration in the mortar is 0.78%, corresponding to a Li : (Na + K) molar ratio of about 4.5.

Table 4: Composition of the lithium slag

Figure 3 shows the expansion in function of time: 0.05% after 14 days, and 0.07% after 28 days. This mixture is thus to be considered as ASR non-reactive, and therefore not subject to ASR degradation.

Example 5: ASR expansion of mortar prepared with lithium-bearing slag (4%)

This example is similar to Example 2, but using a slag prepared according to a process similar to Example 1 for use as Aggregate #2. This slag contains a relatively high amount of lithium, about 4.00% expressed as Li₂0. Its Na₂0 equivalent amounts to 0.15%. It can be calculated that the lithium concentration in the mortar is 1.21%, corresponding to a Li : (Na + K) molar ratio of about 7.8.

Table 5 : Composition of the lithium slag

Li-bearing slag CaO Si0₂ A1₂0₃ Fe₂0₃ MgO K₂0 Na₂0 Li₂0 wt.% 24.31 24.30 38.37 1.34 3.82 0.211 0.01 4.00 Figure 4 shows the expansion in function of time: 0.03% after 14 days, and 0.04% after 28 days. This mixture is thus to be considered as ASR non-reactive, and therefore not subject to ASR degradation.

Claims

1. A process for the production of lithium-bearing concrete, comprising the steps of:

- reduction smelting of lithium-bearing metal scrap, thereby obtaining a metallic phase and a lithium rich metallurgical slag;

- separating the slag from the metallic phase;

- cooling the slag, thereby solidifying it;

- atomizing or comminuting the slag to a powder having a particle size with a D90 of less than 1 mm;

- admixing the powdered slag as aggregate in the preparation of concrete or mortar.

2. Process according to claim 1, whereby the lithium-bearing metal scrap comprises lithium batteries or their scrap.

3. Process according to claims 1 or 2, whereby the concrete or mortar contains more than 0.6 mol of lithium per mol of alkali.

4. Use of a lithium-bearing metallurgical slag as aggregate additive to concrete or mortar for the reduction of the alkali-silica reaction.

5. Use of a lithium-bearing metallurgical slag according to claim 4, wherein the slag is a powder having a particle size distribution with a D90 of less than 4 mm, preferably of less than 1 mm.

6. Use of a lithium-bearing metallurgical slag according to claims 4 or 5, wherein the slag contains at least 2 wt.% of Li₂0.

7. Use of a lithium-bearing metallurgical slag according to any one of claims 4 to 6, wherein the concrete or mortar contains more than 0.6 mol of lithium per mol of alkali.