Reprocessing
ISTRA CAC binders are traditionally used in applications such as building chemistry, sewage pipes, refractory mortars and refractory linings. In addition, ISTRA CAC binders can also be used in special applications in the treatment of liquid and solid wastes. For solid wastes, ISTRA CAC binders can be used to consolidate materials in processes where ordinary Portland cement (OPC) is ineffective.
In waste water processing, ISTRA CAC binders are used because of the binding effect of the soluble calcium aluminate ions with the undesired constituents.
The iron and steel industry often need to introduce materials such as secondary raw materials or their own filter dust back into their process. Unfortunately these materials may have a very small particle diameter (dusty) or have a high residual moisture (sticky). Compaction, by means of briquetting, is often necessary to handle these difficult materials. ISTRA CAC binders offer an excellent solution for compaction of materials such as mill scale and throat sludge that are not efficiently briquetted with OPC.
Briquetting means the process of binding together pulverized, fibrous or lumpy materials, into briquets, often with the aid of a binder and under high pressure. ISTRA CAC binder and waste materials are mixed with water to reach an earth-moist consistancy. The adhesive forces between ISTRA CAC, waste material and water, together with the forming pressure of the briquetting machine (figure 1) provide the green strength of the briquette. After production, the briquettes have to be stored for a certain time to reach their final compressive strength.
ISTRA CAC binders are normal setting but quick hardening Calcium Aluminate Cements with high early strength. They differ substantially from common Calcium Silicate Cements (OPC / Portland Cement), because of their chemical composition and their rapid strength gain. The usage of ISTRA CAC binders may help to increase the throughput of a reprocessing/briquetting plant. With ISTRA CAC binders, waste material compaction can be done even at low temperatures.
ISTRA CAC binders contain Alumina-, Iron- and Calcium- rich minerals. By chosing different ISTRA CAC binders, it is possible to influence the chemical composition of the reprocessed waste material. ISTRA CAC binders are sulphur- and heavy metal-free. Reprocessing of waste materials with ISTRA CAC binders is therefore possible without any SO2 -emission, meeting environmental and legal requirements accordingly. Figure 2 shows rectangular briquettes made of ISTRA CAC and waste material. The size and shape of briquettes may vary according to local requirements.
- figure 1: Labscale briquetting/pavestone device
- figure 2: Briquettes made of ISTRA CAC and waste material
- figure 3: Compressive strength of OPC and ISTRA CAC-Binder
Figure 3 shows the compressive strength of ISTRA CAC and OPC with the same waste material. The briquette made with the ISTRA CAC binder can readily be reintroduced into the process after one day. This is because of the rapid hardening characteristics of our ISTRA CAC binders. However, because of the different hydration mechanism of OPC, the briquette that was made with OPC does not meet the minimum compressive strength requirement of 5 N/mm2. It does not have the necessary mechanical strength to allow for reintroduction into the process.
An additional benefi t of ISTRA CAC binders is provided by their chemical composition. ISTRA CAC binders mainly consist of four oxides. Iron and steel manufacturers, as well as the mineral fi ber industry have a specifi c demand for the chemical composition of their secondary raw materials. Thanks to the different chemical compositions of our ISTRA CAC´s, slag or melt compositions can be adjusted by the right choice from the ISTRA CAC product line.
| ISTRA CAC Type |
Al2O3 |
CaO |
Fe2O3 |
SiO2 |
| ISTRA 40 |
38-42 |
37-40 |
13-17 |
≤ 6 |
| ISTRA 45 |
≥ 44 |
37-41 |
≤ 9 |
≤ 9 |
| ISTRA 50 |
50-53 |
≥ 40 |
≤ 3 |
≤ 6 |
Industrial processes can generate a variety of waste water pollutants, some of which are diffi cult and costly to treat. Waste water characteristics and levels of pollutants vary signifi cantly from one industry to another, and sometimes vary greatly from plant to plant within the same industry. The use of sulfuric acid in battery and fertilizer production as well as in the metal processing and fi nishing industry can generate waste water with high levels of sulfate. Table 2 summarizes the sulfate content of waste water from different industries.
Environmental laws do not classify sulfate ions as pollutants, but the increased salt content inhibits advanced waste water treatment. Sulfates are of considerable concern because they are indirectly responsible for sewer-corrosion problems. Sulfates are reduced to hydrogen sulfi de under anaerobic conditions and lead to sulfuric acid formation (Please see, CALUCEM: “CAC for Sewage Application”). The sulfuric acid corrodes the concrete above the waste water level and leads to a disintegration of the sewage pipe. The concrete corrosion begins at a sulfate concentration of about 600 mg/l and increases with increasing sulfate content in the waste water.
ISTRA CAC is able to remove the sulfate ions from the waste water by precipitating the crystalline compound Ettringite (3 x CaO x Al2O3 x 3(CaSO4) x 32H2O). Ettringite is a non-hazardous solid that binds the sulfate-ions in its crystalline structure. Ettringite has a low solubility of 5 mg/l. Figure 4 illustrates the general steps for waste treatment with ISTRA CAC.
| Industry |
SO42-- Concentration in mg/l |
| Photo Processing |
100000 – 150000 |
| Glass industry |
< 60.000 |
| Mining Waste |
~54000 |
| Metal Treatment |
6000 – 8000 |
| Wire Manufacturing |
4000 – 6000 |
| Battery Factory |
3000-5000 |
| Chemical Plant |
2000-3000 |
Waste water containing SO42- is placed into the mixing tank. ISTRA CAC and hydrated lime are added to the waste water. The ISTRA CAC that is placed into the waste water creates an excess of Ca2+ - and Al3+ -ions. The addition of hydrated lime yields a solution with the pH > 11, the optimum level for Ettringite precipitation. The precipitated Ettringite is then removed from the settling tank after sedimentation. The sulfate level in the waste water can be reduced to < 600 mg/l after treatment with ISTRA CAC.
- Figure 4: Schematic drawing of waste water cleaning with ISTRA CAC
Beside the excellent mechanical strength, wear resistance, ease for repair and less downtime, ISTRA CAC binders offer unique additional porperties in the field of waste treatment:
- Quick Setting and Rapid Hardening
> briquetting is possible even with poor waste materials and at low temperatures
- Increased reprocessing throughput due to quick setting and quick hardening
- ISTRA CAC binders are Alumina- Iron- and Calcium-rich
> Chemical control of solid and liquid waste materials with different ISTRA CAC binders
- Sulphur- and heavy metal-free ISTRA CAC binder solutions
> meeting environmental and legal requirements for processwaste
reprocessing.
We offer customized ISTRA CAC binder solutions for different waste materials. Please contact us for individual consultation.
For additional information about ISTRA CAC binders, please contact us worldwide.
last modified: 28.07.2010
