Proceedings of the 2 nd World Congress on Mechanical, Chemical, and Material Engineering (MCM'16) Budapest, Hungary – August 22 – 23, 2016 Paper No. MMME 120 DOI: 10.11159/mmme16.120 MMME 120-1 Optimal Dosage of Naoh Regarding the Solution Temperature during Corn Starch Gelatinization André Carlos Silva 1 , Débora Nascimento Sousa 2 , Elenice Maria Schons Silva 3 , Thales Prado Fontes 4 , Raphael Silva Tomaz 5 , Mariana Resende Barros 6 1, 3, 6 Federal University of Goiás, Department of Mine Engineering Av. Dr. Lamartine Pinto de Avelar, 1120, Catalão, Brazil ancarsil@ufg.br; eschons@ufg.br; mrezendeb@outlook.com 2, 4, 6 Goiano Federal Institute, Department of Mining Av. Vinte de Agosto, 410, Catalão, Brazil debora.nascimento@ifgoiano.edu.br; thales.prado@ifgoiano.edu.br; raphael.tomaz@ifgoiano.edu.br Abstract - Starches are widely used as depressant in froth flotation operations in Brazil due to their efficiency, increasing the selectivity in the inverse flotation of quartz depressing iron ore. Starches market have been growing and improving in recent years, leading to better products attending the requirements of mineral industry. The major source of starch used for iron ore is the corn starch, which need to be gelatinized, by heat or sodium hydroxide (NaOH) addition, prior its use. This stage has a direct impact on industrials costs, once the lowest consumption of NaOH in gelatinization provides better control of the pH in the froth flotation and reduce the amount of electrolytes present in the pulp. In order to evaluate the influence if the temperature in the NaOH consumption gelatinization tests were carried out with temperatures ranging from 25 to 65 ° C , measuring the volume of NaOH. All tests were performed in triplicate. A linear model correlating the temperature and the NaOH need for the corn starch gelatinization had been stablished. This model can allow mineral industries to optimize the NaOH amount used to prepare the depressant to be used in froth flotation. For example, the reduction in NaOH could easily reaches 480 L per ton of corn starch when performing gelatinization with corn starch solution at 35 ° C when compared to 25 ° C . Keywords: froth flotation, gelatinization, corn starch, sodium hydroxide, temperature 1. Introduction Corn starch is the default depressant for iron ore since 1978. Modified cornstarches are composed by amylopectin (70- 80%) and amylose (20-30%) without impurities such as fibres, mineral matter, oils and proteins normally present in conventional starches [1]. The authors point out that oil (triglycerides) present in conventional starch act as an antifoam agent spoiling the flotation process if its content exceeds 1.8%. The starch’s depressant action is due to the coating of a natural low energy hydrophobic mineral surface with a hydrophilic film to prevent the attachment of air bubbles [2]. Studies showing the importance of the amylose/amylopectin ratio in starch during hematite depression point out that amylopectin reduces the hematite froth flotation more profoundly than amylose when a primary ether amine is used as a collector [3]. The effectiveness of the alkali gelatinization is strongly affected by the starch/NaOH ratio used in the gelatinization [4] and the dissolution technique [5], being the typical ratio 5:1 [4], [6]. Some studies suggest that the starch solution was designed to yield a maximum concentration of 0.1% w/w and must be prepared daily to avoid the retrogradation [7], [8]. However, this is not well stablished and other studies disagree using concentrations up to 3% [9]. The temperature needed for gelatinization decreases with increasing of the amylopectin content. Retrogradation occurs spontaneously when starch solutions are stored at low temperatures at neutral pH. Amylose’s retrogradation may occur within a period of four to five hours after the gelatinization, while the amylopectin retrogrades only 10% within 100 days [10]. The primary adsorption mechanisms of starch on hematite were proposed as non-selective hydrogen bonding and electrostatic forces, mainly because of the presence of a large number of hydroxyl groups in starch molecules and on hematite surface. As confirmed by several studies, starch adsorbs more on hematite surface than on quartz [11]. The adsorption density of starch on quartz surface is approximately 10 times less than that on hematite [12]. For pH’s higher than eight, the starch adsorption is almost non-existent on non-activated quartz surface, while it is noticeable on hematite surface. The reasons for