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ObjectiveTo reduce the content of cadmium in rice， the method of cadmium removal from rice was established and the extraction conditions were optimized by response surface methodology.MethodsThe cadmium extraction rate was used as the index to screen the cadmium removal methods. Commercially available cadmium positive rice was chosen as the test sample and four kinds of food grade organic weak acids were chosen as extractants. The concentration of acid solution， extraction time， solid-liquid ratio and rice powder particle size were used as independent variables to carry out the single factor extraction. And the optimal conditions for removing cadmium from rice was obtained by response surface design.ResultsThe optimal conditions for removing cadmium from rice were 4.2% acetic acid solution， 11 min extraction， liquid-to-material ratio 13：1 （mL/g）， and at least 50 mesh for rice flour. Under these conditions， the average removal rate of cadmium in rice was 98.67%.ConclusionThe experimental model is reasonable and the optimized extraction method is feasible. The removal or reduction of cadmium in raw rice is realized with optimal cadmium extraction conditions， which provides a scientific method for the research on cadmium removal from cadmium-contaminated rice.

An approach for the efficient re-utilisation of waste cement paste powders is proposed, wherein the powders are heated to a certain temperature to prepare regenerated binding materials (RBMs), and then rapidly carbonated by high-concentration carbon dioxide to prepare high-strength products. The structural evolution during the heating process of waste cement paste powder and the carbonation process of RBMs were investigated by X-ray diffraction analysis, scanning electron microscopy and 29Si nuclear magnetic resonance spectrum, and the compressive strength of the carbonated RBM samples was measured. The results show that the differences in carbonation reactivity, carbonation products of the RBMs and properties of carbonated RBMs can mainly be attributed to the differences in the degree of structural order of newly formed β-dicalcium silicate (C2S), the content of β-C2S, free calcium oxide (f-CaO) and incompletely decomposed calcium silicate hydrate (C–S–H) in RBMs. The strength of the carbonated sample of RBM prepared at 1050°C was the highest, followed by that prepared at 950°C, which was significantly higher than those prepared at 650, 750 and 850°C. The content of highly ordered β-C2S in RBMs with high carbonation reactivity and the dense stacking of the carbonation products are beneficial for the mechanical properties. [ABSTRACT FROM AUTHOR]

High-ferrite cement (HFC) has attracted widespread attention due to its advantages, such as low sintering temperature and excellent corrosion resistance. The application of Cu-containing waste in HFC will promote the cement industry toward low-carbon and sustainable development. However, massive amounts of CuO can cause a delay in HFC hydration. The main aim of this paper was to investigate the retardation mechanism of CuO on the hydration of HFC using X-ray diffraction, mercury intrusion porosimetry, isothermal heat-conduction calorimetry, scanning electron microscopy, inductively coupled plasma-optical emission spectroscopy, thermogravimetric analysis and derivative thermogravimetry, among others. The results showed that compared with the undoped clinker, the maximum heat release peak of the clinker doped with 1.5% by weight of CuO was delayed for about 60 h, the hydration induction period was extended from 37 to 89 h, and the compressive strength was zero at 3 days. Through the study of cement suspension at 3 days, it was found that the retardation mechanism is mainly due to the obstruction of Ca leaching. On one hand, the C3S content in the HFC clinker decreases and the grain size of the calcium silicate minerals increases, on the other hand, the Ca2(OH)4·4Cu(OH)2·H2O coats clinker particles at the early stage, leading to a lower hydration degree of the HFC clinker. [ABSTRACT FROM AUTHOR]

Steel slag as an alkaline industrial solid waste, possesses the inherent capacity to engage in carbonation reactions with carbon dioxide (CO2). Capitalizing on this property, the current research undertakes a systematic investigation into the fabrication of high-carbonation precast concrete (HCPC). This is achieved by substituting a portion of the cementitious materials with steel slag during the carbonation curing process. The study examines the influence of varying water–binder ratios, silica fume dosages, steel slag dosages, and sand content on the compressive strength of HCPC. Findings indicate that adjusting the water–binder ratio to 0.18, adding 8% silica fume, and a sand volume ratio of 40% can significantly enhance the compressive strength of HCPC, which can reach up to 104.9 MPa. Additionally, the robust frost resistance of HCPC is substantiated by appearance damage analysis, mass loss rate, and compressive strength loss rate, after 50 freeze–thaw cycles the mass loss, and the compressive strength loss rate can meet the specification requirements. The study also corroborates the high-temperature stability of HCPC. This study optimized the preparation of HCPC and provided a feasibility for its application in precast concrete. [ABSTRACT FROM AUTHOR]