This work is aimed at the development of a semi-continuous mechanochemical process for biodiesel production and the subsequent valorization of glycerol, its by-product, via its conversion into calcium diglyceroxide using the same mechanochemical reactor. This basic solid catalyzes the methanolysis of vegetable oils. The implementation of a semi-continuous process allows both the preparation of the solid catalyst and the methanolysis process, overcoming the miscibility problems of methanol and oil. Thus, a biodiesel yield higher than 90% is reached using a methanol:oil molar ratio close to stoichiometric value and 1.5 wt. % catalyst, after passing through the reactor with a flow rate between 4 and 45 L/h. This new process for biodiesel production can easily be scaled up and applied to the conversion of used cooking oils, without any significant yield decrease. A cost study was also performed, demonstrating that this is more economical than the conventional batch stirring-based process. (C) 2020 Elsevier Ltd. All rights reserved.

Despite the progressive decrease in emissions coming from a variety of sources, lead continues to be one of the toxic metals more often found as environmental pollutants. Of particular concern is lead migration through the soil which may result in contamination of water supplies through;he leaching caused by water infiltration.Carbonate minerals are frequently found in soils and those of heavy metals are usually insoluble so carbonates in the soil could act as a sink for heavy metals for as long as the environmental conditions guarantee their stability. The influence of soil composition on the fixation of lead from aqueous solutions of this metal has been studied. Two clayey soils with different carbonate content have been used in the tests. The kinetics and equilibrium of retention of lead in the soils under different conditions of pH and salinity have been determined using batch and fixed-bed column experiments. Carbonate precipitation and ion exchange were the main processes responsible for the Pb uptake by the soils and concentrations of up to 50% were achieved. The results obtained show that carbonates confer the soil a high immobilization capacity for lead, impeding the advance of the contamination under natural conditions.