Carolina Braccini Freire

Lubricating oils in nuclear power plants may contaminate with radionuclides and become a challenging radwaste for treatment because they decompose in storage and disposal. In addition, conventional methods of immobilization in cement should be checked. This work intends to compare cement and geopolymer used to solidify lubricating oil previously decontaminate using bentonite as sorbent material. Cement is a well-known matrix for radwaste immobilization and geopolymer (alkali-activated material) has been proposed as a new immobilization technology, due to its advantages comparing to cement and bitumen. The geopolymers are cementitious binders formed by aluminosilicates activated in alkaline medium. Synthesis occurs by means of polymerization or polycondensation reactions from the dissolution of SiO44- and AlO45- ions of the aluminosilicates in a highly alkaline solution. After the treatment of the oil radwaste, the contaminated bentonite was immobilized in geopolymer and cement matrix and the final immobilized waste properties were evaluated: compressive strength and homogeneity. The compressive strength result in cement matrix specimens (13,38 MPa) has been higher than in geopolymer matrix (5,96 MPa). Nevertheless, when the homogeneity was compared, the resultant waste in geopolymer presented an aspect more homogeneous than the in the cement matrix. The results showed that the contaminated bentonite was not distributed homogeneously in cement matrix, for this reason the cement was not adequate to solidify the simulated waste. The compressive strength result for the waste in geopolymer matrix did not meet the Brazilian waste acceptance criteria. Therefore, new compositions of geopolymer matrix using less water will be carried out to improve the compressive strength and reach the recommended by Brazilian legislations.

The Iron Quadrangle of Minas Gerais comprises 7,000 km2 and accounts for about 60% of Brazil’s iron ore production. The rocks explored in this region are banded iron formations. The processing of this rock to produce the iron ore concentrate generates large quantities of tailings that were being stored in dams. After the ruptures of the dams in 2015 (Mariana–MG) and 2019 (Brumadinho–MG), dam storage became very difficult. Other storage destinations for tailings are now being considered, including dry storage in piles and the use of tailings as a raw material for other manufacturing chains, such as civil construction and road paving. Due to the fine particle size of the tailings, the use of Portland cement to manufacture products for civil construction is limited. However, alkali-activated cement should play an important role, due to their ability to incorporate fine grained materials. Although alkali activated mortars made with the tailings have good characteristics, their cost is very high, especially when sodium silicate prices are elevated. In this study, sodium silicate synthesis from the tailings, alternative calcined clays, the use of the overburden and other aluminosilicate sources are being investigated with a view to reducing the manufacturing cost. Keywords: Iron ore tailings, Alkali-activated, Building Materials

Among the cementitious materials, geopolymers not only attract interest due to the low emission of CO2 in their manufacturing process, but also because of their good mechanical and chemical properties, together with their resistance to fire. They can be made from different raw materials including various wastes from industrial activities and mineral extraction. In this study, metakaolin was obtained from kaolinite calcined under different conditions. In this case kaolinite is a by-product of sand extraction. It was observed that the calcination conditions (kiln heating rate, calcination time and temperature) had a strong influence on the compressive strength of geopolymer after 28 days of cure. They also affected the composition of the geopolymer, which was prepared by mixing metakaolin, alkaline sodium silicate and sodium hydroxide solution.Compressivestrengthsintherangefrom10MPato50MPamaybeobserved, depending on the combination of these factors. A factorial design of experiments allowed the isolation of the effect of each factor and its interactions, offering new insights into the complexity of the geopolymeric reactions and highlighting the need for a rigid control of the calcination conditions of kaolinite and the composition of the geopolymer samples to obtain the desired compressive strength. Keywords: kaolinite, calcination, metakaolin, geopolymer, compressive strength.

The collapse of the Fundão dam on November 5th 2015 caused impacts along the hydrographic basin of Rio Doce. Renova Foundation has the mission to repair, restore and reconstruct the regions affected by this disaster. After the collapse, a huge amount of waste was deposited in Risoleta Neves Hydroelectric Power Plant’s lake (Candonga). This waste has been dredged out from the lake and deposited in a nearby pile. The use of the waste from this pile is being considered for civil construction. Samples of this waste pile were collected and they were characterized by X-rays diffraction and EDS analyses, which showed that it consists of 80% quartz, 11% hematite, 8% goethite and 1% clays, mainly kaolinite. There is also organic matter consisting of branches, roots and leaves of trees and plants. Previous radiological analyses made before the collapse showed that the radionuclide content of the waste deposited in Fundão dam was very low. However, the waste deposited in Candonga’s lake has a new composition and it is important to evaluate its radioactivity assessment. The analyses results of the Candonda’s waste samples will be presented and compared to the results obtained in the Fundão dam samples, before its collapse.

The use of the sediment deposited in the Candonga dam after the collapse of the Fundão dam is being considered as raw material for civil construction. Blocks were obtained by adding 5 % of sodium carbonate and 13 % of water to the dried dredged sediment, which was mixed and heat treated at 700 ºC and cooled slowly inside the oven to room temperature. The water absorption of the blocks was in the 12-16 % range, the loss of mass in water was (0.01±0.01) %, the density was (1.95±0.03) g/cm³, the compression strength was (11.05±1.29) MPa (reference value ≥ 1.7 MPa), and the flexural strength was (4.42±0.69) MPa (reference value ≥ 3.5 MPa). Small cracks and pores, as well as the growth of white spots (efflorescence) were observed on the surface of the blocks, which can be avoided or attenuated by improving the compaction pressure and the heat treatment.