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Iizuka A.,Tohoku University | Sakai Y.,Seikei University | Yamasaki A.,Seikei University | Honma M.,Nippon Concrete Industries Co. | And 2 more authors.
Industrial and Engineering Chemistry Research | Year: 2012

A bench-scale plant for waste concrete sludge recycling was designed, constructed, and operated. Real concrete sludge generated from a pile and pole production plant and groundwater were used for the experiments. The process mainly consists of the extraction of calcium ions from the concrete sludge into the aqueous phase and the crystallization of calcium carbonate from the solution with CO 2. The CO 2 was supplied from boilers installed in the plant, where heavy oil is combusted. High-purity calcium carbonate (>99%) was obtained in the process, with particle sizes distributed in the range of 3-30 μm (volume-based), peaking at about 10 μm. A net reduction in CO 2 emissions can be achieved based on the process power consumption and the amount of product. The effects of operating conditions on process performance data such as calcium extraction rate and calcium carbonate crystallization rate were examined, which can lead to scaling-up of the plant. © 2012 American Chemical Society.

Iizuka A.,Tohoku University | Honma M.,Nippon Concrete Industries Co. | Hayakawa Y.,Nippon Concrete Industries Co. | Yamasaki A.,Seikei University | Yanagisawa Y.,University of Tokyo
Kagaku Kogaku Ronbunshu | Year: 2012

A new carbon dioxide sequestration process was proposed. The process consists mainly of a calcium extraction step from concrete sludge by water dilution with stirring and a calcium carbonate precipitation step by the reaction of extraction solution and gaseous carbon dioxide. Experimental data for the proposed process was obtained using real concrete sludge generated from a concrete pole/pile plant. The influences of water dilution ratio (weight ratio: 3-50) and extraction treatment time (5-40 min) on the calcium extraction rate from concrete sludge were investigated. It was confirmed that the calcium concentration in water increased sufficiently for calcium carbonate to be precipitated by the reaction with gas containing carbon dioxide (10%). In the range of experimental conditions studied, the dilution ratio of 20 and the extraction time of 5 min were found to be the optimal treatment conditions for calcium extraction from concrete sludge. The calcium carbonate precipitation step from calcium solution is easily accelerated by the addition of seed crystals. These results indicate that concrete sludge can be used as a cheap calcium resource for carbon dioxide sequestration. © 2012 The Society of Chemical Engineers, Japan.

Sasaki T.,Seikei University | Iizuka A.,Tohoku University | Honma M.,Nippon Concrete Industries Co. | Yoshida H.,Nippon Concrete Industries Co. | And 3 more authors.
Kagaku Kogaku Ronbunshu | Year: 2014

A solid material prepared from concrete sludge, PAdeCS®, an industrial waste consisting of surplus concrete from concrete product industries and construction sites, was applied to a phosphorus recovery process with a packed-bed flow system. Sieved particles of PAdeCS were packed in a plastic column, and a model wastewater of pH 7 containing 100 mg-P/L of potassium dihydrogen phosphate (KH2PO4) was fed into the column. The concentration of phosphorus in the effluent solution remained as low as about 0.1 mg-P/L before the breakthrough time and increased rapidly thereafter. The amount of model wastewater that can be treated by the present system was found to increase with the height of the packed layer. The removal of phosphorus is thought to occur by the formation of hydroxyapatite (HAP) from calcium ions and hydroxyl ions dissolved from the hydrated cement components in PAdeCS and phosphorus ions in the model wastewater. The formation of HAP occurred at the surface of the packed layer of PAdeCS as well as the formation of HAP crystals in the bulk solution phase. The ratio of HAP formation, which is equivalent to the phosphorous recovery ratio, was found to depend on the height of the PAdeCS layer and the flow rate of the model wastewater. © 2014 The Society of Chemical Engineers, Japan.

A dephosphorization material is formed from concrete sludge resulting from centrifugal casting of concrete products, production of concrete, cleaning of concrete production equipment, or cleaning of concrete transporting vehicles. The dephosphorization material is used for dephosphorization treatment by a dephosphorization apparatus that includes a single reaction tank provided with a wastewater supply means, a dephosphorization material supply mean, and a recovery means. The dephosphorization apparatus removes phosphorus from phosphorus-containing wastewater, such as sewage water, based on the formula 10Ca^(2+)+6PO_(4)^(3)+2OH^()Ca_(10)(PO_(4))_(6)(OH)_(2 )and recovers through the recovery means a dephosphorization by-product that precipitates as crystals as a result of the reaction.

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