Preparation of Biological Ceramsite from Tungsten Tailings

Feng Xiujuan from Huazhong University of Science and Technology conducted an experimental study on the preparation of porous biological ceramsite filter media using the roasting method, with tailings from the Daxiao Longxia tungsten mine in Jiangxi as the main raw material, and furnace slag, fly ash, and clay as auxiliary materials. The main chemical composition of the tailings used is shown in Table 8‑1. Other auxiliary materials included concentrated hydrochloric acid, furnace slag, fly ash, clay, pore‑forming materials (sawdust or foam plastic), a binder (modified starch), acrylic resin‑based white coating, xylene solvent, etc.

Table 8‑1 Main chemical composition of tungsten tailings (wt%)

Figure 8‑1 Process flow diagram for the preparation of biological ceramsite

The preparation process flow of biological ceramsite from tungsten tailings is shown in Figure 8‑1. The tailings were first modified with a 20% hydrochloric acid solution to create a large number of pores. The modified tailings were then mixed and stirred uniformly with furnace slag, fly ash, and clay in a certain proportion, with a small amount of pore‑forming material and binder added. The mixture was formed into spherical ceramsite green pellets using a granulator. The green pellets were placed in an electric constant‑temperature drying oven at 120 °C for 1 h, then transferred to a muffle furnace. The temperature was gradually raised to 500 °C within 1 h, held at that temperature for 10 min, and then increased to 800–1200 °C for roasting for 30 min. After roasting, the product was taken out and allowed to cool naturally to room temperature. The roasted product was placed in a ball mill and polished by self‑grinding. Then, an acrylic resin‑based white coating diluted with xylene was sprayed onto the surface using a spray gun. After drying at room temperature, the final biological ceramsite product was obtained. During the spraying process, the pressure of the air compressor was maintained at 0.2–0.5 MPa, the atomization angle of the spray gun was 30°–50°, the distance from the nozzle to the ceramsite was 15–50 cm, the room‑temperature drying time was 0.5–1.5 h, and the dry film thickness of the coating was 20–30 μm.

The experimental results showed that when the volume ratio of tungsten tailings, furnace slag, fly ash, and clay was 4 : 1.5 : 1.5 : 1 and the roasting temperature was 1100 °C, the prepared biological ceramsite had a particle density of 1.61 g/cm³, a bulk density of 1.10 g/cm³, a specific surface area of 9.7 m²/g, an acid solubility of 0.17%, an alkali solubility of 0.33%, and a cylinder compressive strength of 8.1 MPa. When this biological ceramsite was used to treat actual wastewater with a chemical oxygen demand (COD₍Cr₎) of 817 mg/L, it exhibited fast biofilm formation, high microbial attachment, and easy backwashing. The COD₍Cr₎ removal rate reached over 93% within 20 days.

Preparation of Biological Ceramsite from Iron Tailings

Zhang Xuedong et al. from Tangshan College conducted a study on the preparation of biological ceramsite filter media using iron tailings as the main raw material, with the addition of auxiliary materials such as furnace slag, fly ash, limestone, and admixtures.

8.2.1 Raw Materials

• Iron tailings: Obtained from an iron mine in Qian’an, Tangshan. They are the main raw material for ceramsite, providing strength and serving as a binder.
• Furnace slag: Taken from coal‑fired boiler waste residue, which provides partial calorific value and also acts as a pore‑forming agent for the ceramsite.
• Fly ash: Sourced from the Tangshan Power Plant, which improves the pelletizing performance.
• Limestone: Acts as a pore‑forming agent and also enhances the strength of the ceramsite during calcination.
• Admixture: Mainly composed of organic substances, functioning as both a pore‑forming agent and a binder.

The chemical compositions of the main raw materials are shown in Table 8‑2.

Table 8‑2 Main chemical composition of ceramsite raw materials (wt%)

8.2.2 Preparation Process

The raw materials were accurately weighed according to a specified ratio and placed in a cement paste mixer. 27% tap water was added and mixed uniformly. Green pellets of 3–5 mm in diameter were produced by manual pelletizing. The pellets were dried at 105±5 °C for 3 h to remove free water, and then placed in a high‑temperature resistance furnace. The temperature was raised according to a programmed heating schedule to 1100 °C and calcined for 30 min. After calcination, the ceramsite products were naturally cooled to room temperature to obtain the iron‑tailings biological ceramsite.

Through wastewater treatment experiments, the optimal raw material ratio was determined as: iron tailings 86%, furnace slag 7%, fly ash 5%, limestone 1%, and admixture 1%. Under the calcination temperature of 1100 °C, the prepared ceramsite had a rough surface, particle size of 3–5 mm, water absorption of 14.01%, porosity of 31.07%, bulk density of 1.12 kg/m³, and apparent density of 1.92 kg/m³. The turbidity removal rate for domestic wastewater reached 64.02% within 30 h, and the COD₍Cr₎ removal rate was as high as 79.48%, showing significant effectiveness.

Wang Demin et al. from Wuhan University of Science and Technology prepared porous ceramsite with a tailings addition rate of up to 77% using a low‑silicon iron tailings as the main raw material. The treatment performance of the prepared ceramsite on simulated domestic wastewater was investigated using a laboratory‑scale biological aerated filter (BAF). The results showed that the ceramsite had a rough surface and abundant internal pores, with apparent density, apparent porosity, and average pore diameter of 1.33 g/cm³, 54%, and 19.80 μm, respectively. The heavy metal concentrations in the leachate from the heavy metal leaching test met the national surface water quality standards. The BAF using this ceramsite as filter media performed well in treating simulated wastewater, with removal rates of COD₍Cr₎, NH₄⁺‑N, and TN reaching 84.26%, 84.01%, and 25.87%, respectively. The microorganisms attached to the ceramsite in the filter column were rich in species, and the total biomass phosphorus per unit mass of ceramsite at the influent end reached 371.63 nmol/g, with 90.79% distributed on the surface and 9.21% inside the ceramsite.

8.3 Preparation of Biological Ceramsite from Lead‑Zinc Tailings

Wang Shuncai et al. from Hohai University used lead‑zinc flotation tailings as raw material, with sodium silicate and lignin as additives, to prepare water‑treatment ceramsite by high‑temperature roasting, and conducted experimental studies on its adsorption performance for beneficiation wastewater.

The tailings used in the experiment were flotation tailings from Nanjing Yinmao Lead‑Zinc Mining Co., Ltd. The main minerals in the tailings were silicates, along with some oxides of Fe, Mn, and Al, and the loss on ignition was 18.93%. The preparation process of the ceramsite was as follows: 30 g of whole tailings were weighed into a beaker, and a certain volume of distilled water was added and mixed uniformly. The mixture was formed into small balls of 5–10 mm in diameter using a disc pelletizer. The pellets were dried in an electric blast drying oven at 105 °C for 2 h, and then placed in a high‑temperature box‑type electric furnace controller and roasted at a certain temperature for 2 h. The furnace was then turned off and the ceramsite was allowed to cool inside the furnace for 12 h before being taken out.

The experimental results showed that the ceramsite prepared from whole tailings roasted at 800 °C exhibited good adsorption performance for COD₍Cr₎ in beneficiation wastewater. The optimal adsorption time was 30 min, the optimal temperature was room temperature, the optimal dosage was 2 g/100 mL, and the optimal pH was about 8. The COD₍Cr₎ removal rate and adsorption capacity reached 87.1% and 17.85 mg/g, respectively. To reduce tailings detachment and increase the strength of the ceramsite, experiments with binder addition were also conducted. Through tests on the effect of different binders on adsorption performance, the binders chosen were sodium silicate and lignin, with an addition amount of sodium silicate (2.5 g) + lignin (2.5 g) per 30 g of tailings. The water‑treatment ceramsite prepared by roasting at 800 °C for 2 h had sufficient strength to resist erosion by water flow, and its adsorption capacity reached 22.84 mg/g.