Abstract Flocculation is a complex process, usually dependant on various conditions to perform adequately. Nevertheless, the relevance and interaction of the process variables are not easily found in literature. In this study, nine variables of ultrafine quartz flocculation systems, defined in Part 1 of this study, were analysed. The effects of each variable and their interactions in the system were investigated based on flocculation and sedimentation tests. The results were statistically evaluated using the supernatant turbidity as experimental response. The evaluations resulting from the statistical approach indicated that suspension pH (5.49%) was the most significant variable, followed by flocculant concentration (4.07%) with the second greatest effect on the turbidity of the supernatant. Solid concentration, agitation intensity, and surfactant conditioning time (4.05%, 3.51% and 3.51%, respectively), also have significant effects on ultrafine quartz flocculation. The flocculant concentration and the surfactant conditioning time were the variables with the most significant interactions with the main variables. The Camp Number values showed a negative exponential relationship with the turbidity results, proving to be an important tool to evaluate flocculation. Backscattered electron scanning microscopy images of flocs formed in the presence of 30 g/t PAM showed compact flocs in the size range between 150 and 365 µm, with noticeable sphericity.

Abstract A characterization study was performed to verify the more relevant physicochemical properties for quartz flocculation with polyacrylamide, as well as to define which variables should be further investigated regarding this flocculation system. Polyacrylamide was evaluated through molecular weight, radius of gyration, and infrared spectrometry. A natural quartz sample was investigated regarding its particle size distribution, specific surface area, mineralogical and chemical composition. The zeta potential of quartz with flocculant and surfactant was also analyzed. The results indicated that the quartz had high purity and particle sizes between 38 and 10 µm, which was within the intended particle size range; the flocculant presented a suitable molecular weight for the proposed flocculation system. Based on literature, nine variables were chosen to be investigated in Part II of this study: flocculant and surfactant concentration, flocculant and surfactant conditioning time, flocculation addition time, agitation intensity, pH of the suspension, flocculation time, and solid concentration.

Abstract Sinergy is the interaction of two or more agents to produce a combined effect greater than the sum of their separate effects. Etherdiamine yields superior results for quartz floatability in a Hallimond tube and higher selectivity in the reverse bench scale cationic flotation of an iron ore, when compared to ethermonoamine. Blending these collectors yields better results than each one used individually characterizing a synergistic effect. This work evaluated the effects of the collectors ethermonoamine, etherdiamine and the mixture of these at the ratio 1:1 on the flotation of the quartz through the microflotation and bench flotation tests with a typical Brazilian iron ore. The results demonstrated the occurrence of synergistic effects in tests performed at concentrations of 1 and 3 mg/L and pH 10.5, in the absence of a depressant. In the presence of a depressant, the synergy was not observed under the same tested conditions, due to the collector-depressant interaction. On other hand, the bench flotation tests indicated the occurrence of synergy regarding silica content in the concentrate while an additive effect was observed for the iron recovery and Selectivity Index index demonstrating that a feasibility of using collector mixtures in this process, was not clearly achieved on the tested ratio 1:1.

Abstract A bench scale study was carried out to investigate the influence of polyacrylamides as co-depressant in a blend with starch depressant on the reverse cationic iron ore flotation. The results indicated that the use of polyacrylamides as dual function polymer should be an alternative to improve the flotation process. These polymers act as a depressant and flocculant reagent, decreasing the mechanical entrainment of hydrophilic iron minerals, forming hydrophobic aggregates. Also, the use of polymers as a co-depressant could prevent the possibility of clathrate formation caused by starch and amine overdose. The results obtained showed that cationic and non-ionic polyacrylamides improve the selectivity when applied at low dosages. Only the slightly charged anionic polyacrylamide yielded good results in flotation tests. The design of experiments carried out with non-ionic polyacrylamides showed that flotation results was were affected by the physico-chemical conditions of the system, such as pH, flocculant molecular weight and amine type.

Abstract In the present study, microflotation experiments were performed on pure minerals systems involving hematite and quartz in the presence of etherdiamine as collector. The influence of polyacrylamides as co-depressant was investigated in a blend with starch depressant. The results obtained demonstrated that all the polyacrylamides used were efficient in hematite depression, at different levels and following the order of effectiveness: cationic > non-ionic > anionic. The depressant power was proportional to the degree of ionicity and the molecular weight. It is proposed that the enhanced performance is due to the presence of two functional groups, the cationic group adsorbing by electrostatic interaction and the amide group –C(=O)NH2 adsorbing by hydrogen bonding. Non-ionic polyacrylamides indicated similar performances for different molecular weights and the proposed adsorption mechanism is hydrogen bonding associated with the amide group. Electrostatic repulsion did not have deleterious action on the adsorption of anionic polymers on hematite, nevertheless the adsorption on quartz was impaired. Polyacrylamides adsorb on quartz, although at a weaker intensity than on hematite.

Abstract The inefficiency in controlling the slurry/froth interface level of a scavenger column flotation stage was severely impairing the process performance of an iron mining company, increasing the iron content in the tailings to levels above 20% and, consequently, not meeting the company's iron recovery and pellet feed production targets. Based on mass balance and process data, hydraulic calculations were performed and showed that the installed 6.0" (15.24cm) diameter barometric leg tubes and the control system valve were adequate. An equation to determine the maximum barometric leg height was developed for the flotation column and other calculations showed the necessity to reduce this height from 4.6m to a maximum of 3.4m. The barometric leg adequacy considerably decreased the variability in controlling the slurry/froth interface level, reduced the iron content in the tailings from 24.9% to 18.9% and increased the iron recovery in the flotation stage from 97.9% to 98.7%.

Abstract Quartz floatability in cationic reverse flotation depends on the suitable choice of surfactant type and the conditions under which they are applied. The design of experiments (DOE) allows the evaluation of process variables, in a structured and independent way, with statistical validation and a limited number of tests. Tests of microflotation of quartz, in the size range -150 +75 µm, using factorial design of experiments, showed that etherdiamine leads to higher level of quartz floatability than ethermonoamine, favored by increase in collector concentration, at the high level of pH tested (11.0). Floatability values above 90% were achieved with the use of 3 mg/L of ether diamine for both pH levels, while with ether monoamine the target was reached only at pH 11.

Abstract Flotation plays a relevant role in the concentration of iron ores. Conventional flotation technology employing mechanical machines and columns and also circuits combining both types of cells have been utilized in the iron ore industry. The top size of particles in the flotation circuit feed is 150 µm and the slimes below 10 µm are removed as overflow in hydrocyclone classification. The conventional flotation technology faces difficulties in achieving tailings with iron grades lower than 12% and concentrates with SiO2 grades lower than 1%, and requires long residence times, resulting in large volume machines and huge footprints. The pneumatic flotation technology was evaluated in the reverse flotation of quartz from an iron ore sample of the Iron Quadrangle, Brazil. Bench and industrial scale tests were conducted in pneumatic flotation machines at low residence time. Both tests were carried out in open circuit stages with the objective of comparison with mechanical cells. The bench scale tests were carried out in three stages (rougher, cleaner and recleaner) in an 11 L pneumatic cell aiming at final concentrate with maximum 2% SiO2 while the industrial tests were carried out in a 25 m3 pneumatic cell in the rougher stage aiming at comparison with a circuit of five 14 m3 cells in the rougher stage and four 14 m3 cells in the scavenger stage. The collision and particle-bubble adhesion occur in a step before the pulp reaches the pneumatic cell vessel. The results indicate the possibility of achieving concentrates with a SiO2 content of approximately 1% and tailings with iron contents lower than 10% with three stages (rougher, cleaner and recleaner) without the need of scavenger stages. Furthermore, the residence time was three times shorter than that required for conventional mechanical cells. The speed of the pulp at the entrance of the pneumatic cell strongly affects the quality of the concentrate.

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. The starch market has been growing and improving in recent years, leading to better products attending the requirements of the mineral industry. The major source of starch used for iron ore is the cornstarch, which needs to be gelatinized, by heat or sodium hydroxide (NaOH) addition (also known as caustisized starch), prior its use. This stage has a direct impact on industrials costs, since the lower consumption of NaOH in gelatinization provides better control of the pH in the froth flotation and reduces the amount of electrolytes present in the pulp. In order to evaluate the influence of temperature on the NaOH consumption, gelatinization tests were carried out with temperatures ranging from 25 to 65 ºC, measuring the volume of NaOH. All tests were performed in triplicate. A linear model correlating the temperature and the NaOH need for the cornstarch gelatinization has been stablished. This model can allow mineral industries to optimize the NaOH amount used to prepare the depressant used in froth flotation. For example, the reduction in NaOH could easily reach 480 L per ton of cornstarch when performing gelatinization with the cornstarch solution at 35 ºC instead of 25 ºC (reduction of approximately 34% in the NaOH consumed).

Abstract This paper presents a potential condition to separate kaolinite through flotation when it is present in bauxite ore. This research anticipates a Brazilian industry requirement, considering the tendency towards the need for aluminosilicates removal from bauxite ores, as has already occurred in China. Kaolinite is the most abundant aluminosilicate, and gibbsite is the main aluminum bearing mineral in Brazilian bauxite ores. The first step was a fundamental study involving microflotation experiments with pure samples of kaolinite and gibbsite. Ammonium quaternary salts and amines were used as the collector and corn starch as the depressant. In a fundamental study, the best conditions determined in the first step were evaluated for the flotation of kaolinite from bauxite ore using laboratory scale experiments. Tests with AQ142/starch (pH 10) and CTAB (pH 7) led to satisfactory results. In general, the highest values of alumina/silica mass ratio were obtained with AQ142/starch and the highest values of mass recovery and metallurgical recovery were achieved with CTAB.

Abstract The dispersion degree of the mineral particles in the pulp is especially relevant regarding the performance of the cationic reverse flotation of iron ores. The gangue minerals should remain dispersed while hematite particles should be selectively flocculated. The present study addressed determinations of dispersion degree and zeta potential of hematite in the presence of different dispersants, classified as organic polymeric (natural and synthetic), organic monomeric, and inorganic. Special attention was paid to results achieved at pH 10, used in plant practice. For natural organic polymers, correlation was observed between the dispersion degree and the increase in the negative value of zeta potential. Some synthetic organic polymers enhance the dispersion of hematite particles despite not affecting significantly the zeta potential. Sodium silicates, irrespectively of the SiO2/Na2O ratio, at pH 10, did not impact significantly either the dispersion degree or the zeta potential.

Abstract In iron ore pelletizing plants a range of process parameters such as particle size distribution, specific surface area, and moisture, must be controlled to achieve optimized operation conditions. Particle size distribution and specific surface area are controlled during the grinding operations. Moisture, however, is controlled during filtration of the ground products. This work investigates the relationship between particle morphology, filter cake moisture and filter capacity. The samples were taken during the filtration tests and referred to three different blends presenting distinct mineralogical features and similar chemical compositions in order to investigate the effects of only the hematite surface characteristics. Six types of morphology are distinguished: granular hematite, tabular hematite, martitic hematite, polycrystalline hematite, hematite-goethite aggregates and goethite. For each filtration test, the filter cloth product was characterised. The characterisation analysis revealed that blends containing martitic hematite concentration above 11.45 percent increased substantially the filter capacity. However, it had also caused an increasing in final moisture content that reached values around 10.0 % compared with industrial moisture specification that can vary on the range of 8.5 to 9.5 %.

A forte demanda por bens minerais verificada nas últimas décadas tem levado o setor mineral a ampliar sua capacidade produtiva. Diferentes métodos de concentração têm sido propostos para separação seletiva da apatita dos contaminantes carbonatos e silicatos presentes em minérios fosfáticos. Separação magnética, hidrogravimétrica e calcinação são métodos que apresentam baixa eficiência e custo elevado. A flotação é o método mais indicado, porém a seletividade é dificultada devido à similaridade da composição química superficial entre fosfatos e carbonatos, a alta atividade superficial dos coletores utilizados, interações entre espécies iônicas dissolvidas de um mineral sobre outro e, também, entre espécies iônicas dissolvidas e reagentes. Nesse estudo, realizado em laboratório, oito diferentes depressores, orgânicos e inorgânicos, foram testados na flotação aniônica direta de um fosfato sílico-carbonatado. O melhor desempenho foi obtido com fécula de mandioca, que exerceu boa depressão sobre a calcita e os silicatos.

A high demand for mineral resources observed in recent decades has led to an expansion in production in the mining industry. Different process alternatives have been proposed for selective separation between apatite and contaminants (carbonates and silicates) present in phosphate ores. Magnetic separation, calcination and gravity separation processes are methods that present low efficiency and high cost. Flotation is the most common process; however the selectivity is hampered by the superficial similarity of the chemical composition of phosphates and carbonates, high surface activity of the collectors used, interactions between dissolved ionic species of certain mineral with another and also interactions between dissolved ionic species and reagents. In this study, conducted in a laboratory scale, eight different depressants, organic and inorganic, were tested in the direct flotation of a Brazilian silicate-carbonate phosphate ore. The best performance in the depression of calcite and silicates was achieved with cassava starch.

A otimização de circuitos industriais de moagem tem sido realizada com sucesso, utilizando-se modelos matemáticos que relacionam dados industriais com parâmetros de quebra determinados através de testes de moagem em escala de laboratório. O material estudado é um minério de ouro moído através de um circuito fechado de moagem de bolas. A classificação foi realizada por hidrociclones. Várias campanhas de amostragens foram realizadas com o objetivo de fechar um balanço de massas e fornecer material para os testes em laboratório. Os parâmetros determinados nos testes em laboratório, foram utilizados para prever, por simulação, o comportamento do circuito operado com baixo enchimento de bolas e com distribuição balanceada de tamanhos de bolas.

The optimization of industrial grinding circuits has been successfully performed using mathematical models that describe the industrial scale data from breakage parameters determined in laboratory grinding tests. The test material studied here is a gold ore ground in a closed ball mill circuit with hydrocyclone classification. Several sampling campaigns were carried out aiming to produce mass balances and provide material for laboratory tests. The parameters determined in the laboratory tests were used to predict, by simulation, the circuit behavior with a low ball charge level and a balanced ball size distribution.

A recuperação de minerais portadores de ferro, a partir de rejeitos de beneficiamento de minérios de ferro, representa um desafio quanto à sustentabilidade do estágio preliminar da siderurgia. Essa investigação abordou a produção de concentrado de minério de ferro dentro das especificações de pellet feed da Samarco, a partir de amostra representativa do overflow dos ciclones deslamadores (101,6mm, 4") do concentrador I da Samarco. Os ensaios incluíram estágios de microdeslamagem e flotação. O método de microdeslamagem desenvolvido mostrou-se eficiente e o concentrado produzido por flotação catiônica reversa apresentou teor de sílica compatível com o exigido para pellet feed.

The recovery of iron bearing minerals from the reject products of the beneficiation of iron ores is a challenge concerning the sustainability of the preliminary stage of iron and steel making. This investigation addressed the production of iron ore concentrate within the specifications of Samarco's pellet feed from a representative sample of the concentrator I desliming cyclone's (101.6 mm, 4") overflow. The experiments included stages of microdesliming and flotation. The developed microdesliming method was efficient and the concentrate produced via cationic reverse flotation presented silica content compatible with pellet feed requirements.