۱٫ Introduction

۲٫ Materials and methods

۳٫ Results and discussion

۴٫ Conclusions

Abstract

This study aims at investigating the possibility of using smectite clay waste, generated during the oil bleaching process as an additive for Portland cement. The smectite clay waste consists of montmorillonite, quartz, anorthite, calcium sulfate, and amorphous phase. For the regeneration of this waste, the extraction with hexane and thermal method were chosen. The results showed that the extraction of smectite clay waste with hexane significantly increased the pozzolanic activity of this waste; however, the extracted additive prolonged the induction period of Portland cement hydration, slowing down initial cement hydration, and reduced the compressive strength of Portland cement samples.

The thermal activation method achieves the best results by calcining smectite clay waste at 600 °C. The calcined additive indicated the strong pozzolanic activity. However, this phenomenon is associated with the formation of the amorphous phase by activating the smectite clay with the sulfuric acid rather than the degradation of the clay minerals during the combustion. The calcined smectite clay waste (CSCW) accelerates the hydration of calcium silicates in the second period of the exothermic reaction. The results of the investigation showed that in samples with the CSCW additive proceed the intense pozzolanic reaction, which can be clearly identified after 28 days of hydration. Up to 15 wt% of the Portland cement can be replaced by the smectite clay waste additive calcined at 600 °C without reducing the compressive strength of Portland cement samples.

Introduction

Nowadays one of the most current issues is the environmental pollution caused by industrial waste, which is being produced by large-scale production in various industries. Only a small part of the industrial waste is recycled and its application in other industries is highly important. Various studies have shown [1-5] that some industrial waste can be used by replacing a part of the clinker in cements or a part of the cement in concrete. In this case, when the waste is used as an additive for 32 binding materials, not only the pollution issue is solved but also the cost of Portland cement or concrete is decreased.

Oil bleaching is one of the processes applied in oil industry during which the impurities that add colour to the oil are removed and oil is purified from carotenoids, peroxides, chlorophyll, etc. Oils are bleached using a powdered, surfactant materials, which are called bleaching earths. Bleaching earths can composed of up to different types of clay minerals, such as smectite, bentonite, attapulgite and sepiolite. The bleaching process is carried out under vacuum, with temperature in the range of 80-120 °C and contact time ranging from 20-40 min. The dosage of bleaching earth usual is 0.5-2 % by weight. After bleaching, the mix of clay and oil are separated by the vacuum filtration into two phases: oil and clay waste. As a consequence, the oily clay becomes hardly recycled waste. Market demand for activated bleaching earth was predicted to rise to ~9M/year tones until 2022, therefore, the amount of waste produced through the edible oil bleaching process, is considerable [6].