Utilization of Gaseous Carbon Dioxide and Industrial Ca-Rich Waste for Calcium Carbonate Precipitation: A Review

Calcium carbonate synthesis from Kambara reactor desulphurization slag via indirect carbonation for CO2 capture and utilization

In this work, industrial Kambara reactor desulphurization slag (KR slag) was indirectly carbonated. The effects of leaching time, leaching temperature, leaching agent types, and leaching agent concentration on the leaching ratio of calcium from KR slag were investigated. Subsequently, precipitated calcium carbonate (PCC) was synthesized by bubbling CO2 gas (flow rate of 15 mL/min) into 400 mL leaching solutions at 40 °C for 120 min with magnetic stirring at 300 rpm. It is found that calcium in KR slag can be selectively extracted using a diluted solution of ammonium acetate (CH3COONH4) or ammonium chloride (NH4Cl), while ammonium sulfate ((NH4)2SO4) solution is not suitable as leaching agent due to the formation of slightly soluble calcium sulfate (CaSO4). The leaching ratio of calcium is improved by extending the leaching time or increasing the leaching solvent concentration. However, leaching temperature has little effect on calcium extraction. After carbonating the NH4Cl- and CH3COONH4-leachate for 120 min, calcite and vaterite type PCC with a purity of 99% is synthesized. Each gram of KR slag can produce 0.794 g and 0.803 g PCC using NH4Cl and CH3COONH4 leaching agents respectively. Calculations show that 349.6 kg CO2 is captured by per ton of KR slag. The CO2 capture capacity of KR slag is significantly higher compared with previously studied materials.

Valuable Biodiesel Catalyst from Solvay Wastewater

Biodiesel is considered a renewable, green fuel as it is derived from renewable living resources like animal fats or vegetable oils. This research is utilized to investigate the possibility of using Solvay wastewater as a source of biodiesel catalyst, which is CaO. CaCl2 from Solvay wastewater reacts with CO2 to produce CaCO3. CaCO3 is then heated to produce pure CaO. Waste cooking oil, wastewater, and CO2, which are considered dangerous materials to the environment, are used to produce valuable products. This research has environmental and economic benefit benefits of using waste materials as a replacement for raw materials. The selected experimental parameters for the CaCO3 production step are stirring rate (500–1300) rpm, CO2 gas flow rate (900–2000) mL/min, amount of ammonia (15–35) mL, and glycerol volume (0–25) mL. The selected experimental parameters for the biodiesel production step are reaction time (2–6) h, methanol to oil ratio (9–15), catalyst loading (1–5) %, and reaction temperature (50–70) °C. The impact of reaction parameters on reaction responses was assessed using the response surface methodology technique. A formula that represents the reaction response as a function of all the independent factors has been created. The optimization of the process is done in two steps: the first one is for the CaCO3 process while the second one is biodiesel production optimization. The first optimization was done to get the CaCO3 with minimum particle size and yield. The second optimization was done to get the maximum amount of biodiesel using minimum energy and low reaction conditions. Process optimization resulted in another economic benefit for this research. The resulted biodiesel yield equals 95.8% biodiesel yield at 2 h reaction time, 15:1 molar ratio of methanol to oil, 56 °C reaction temperature, and 1% catalyst loading.

A review on the applications of microbially induced calcium carbonate precipitation in solid waste treatment and soil remediation

Improper disposal and accumulation of solid waste can cause a number of environmental problems, such as the heavy metal contamination of soil. Microbially induced calcium carbonate precipitation (MICP) is considered as a promising technology to solve many environmental problems. Calcium-based solid waste can be utilized as an alternative source of calcium for the MICP process, and carbonate-based biominerals can be used for soil remediation, solid waste treatment, remediation of construction concrete, and generation of bioconcrete. This paper describes the metabolic pathways and mechanisms of microbially induced calcium carbonate precipitation and highlights the value of MICP for solid waste treatment and soil remediation applications. The factors affecting the effectiveness of MICP are discussed and analyzed through an overview of recent studies on the application of MICP in environmental engineering. The paper also summarizes the current challenges for the large-scale application of this innovative technology. In prospective study, MICP can be an effective alternative to conventional technologies in solid waste treatment, soil remediation and CO₂ sequestration, as it can reduce negative environmental impacts and provide long-term economic benefits.

Study of the Effect of Leucine on Calcium Carbonate Precipitation in a Circular Economy Perspective

This paper studies the crystallization of calcium carbonate in the presence of leucine—a green additive. The effect of leucine on calcium carbonate precipitation kinetic is particularly interesting since CaCO3 is a valuable product worthy to be recovered from industrial liquid wastes (e.g., desalination brines) in the circular economy approach. Experiments have been performed in a laboratory scale plant with a supersaturation range which spams from 2 to 120 and two different leucine concentration (0.520 × 10−3 and 1.041 × 10−3 mol/L). Results obtained have been compared with previous published ones, carried out without any additives. From the measurements of induction times for calcium carbonate nucleation, it was established that in solution, the leucine favors the precipitation of calcium carbonate, so it can be considered a promoter in calcium carbonate crystallization and this behavior enhances when raising its concentration in solution. Interfacial tension was determined for both leucine concentration levels, and the values obtained are in the range 51–84 mJ/m2.