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Influences of magnesium ions in water on gelatinization characteristics of starch and its flocculation behaviors on particles

Tang Min, Niu Xiaoying, Wen Shuming

Physicochemical Problems of Mineral Processing

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2024

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Vol. 60, iss. 1

art. no. 178149

EN

It is inevitable for the occurrence or built-ups of disturbing cations, especially Ca2+ or Mg2+ ions, in process water during the flotation of iron oxides by using starch as flocculants. In addition to alkali concentrations and temperature, water quality could have an essential role in changing the physicochemical properties of the starch solution and consequently disturbing its flocculation performance on particles. This study aims to identify the effects of magnesium ions on the gelatinization characteristics of starch and its flocculation properties on particles through a series of tests, such as flotation tests, settling tests, size analyses, zeta potentials, powder contact angle, Fourier Transform Infra-Red (FTIR) and X-ray Photoelectron Spectroscopy (XPS) measurement. All results show that magnesium ions at ≤ 4 mmol/L have a positive role due to enlarging the sizes of the particle flocs and accelerating their settling rates. The occurrence of Mg2+ ions at higher concentrations during starch gelatinization only obtains a starch sol-gel with entangled configurations and preoccupied active sites, resulting in the slower settling rate of the particle flocs and less hydrophilicity on mineral surfaces. It could be attributed to the cross-link interactions of magnesium-based precipitates with the acidic groups, especially carboxyl groups on the starch remnants. The suitable acid/base interactions between Mg(OH)2/MgCO3 compounds with these groups in the starch suspension could be beneficial for enhancing the flocculation of hematite as they could build bridges among the pieces and enlarge their sizes as a “load carrier” for aggregation with minerals. However, too much cross-linking could reentangle the remnants, block their adsorption sites on mineral surfaces, and eventually, weaken the flocculation capacity of starch.

2

Effects of Ca2+/Mg2+ ions in recycled water on the reverse flotation properties of iron oxides

Tang Min, Yan Wu, Fu Jiahao

Physicochemical Problems of Mineral Processing

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2024

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Vol. 60, iss. 3

art. no. 188465

EN

Water quality, particularly hardness, plays an important role in affecting the floatability of minerals as it interferes with the chemical/electro-chemical characteristics of mineral surfaces and their interactions with flotation reagents. It could become unpredictable when water sources characterized by different calcium or magnesium ion distributions were involved. This study aimed to identify the role of Ca2+/Mg2+ ions in the recycled water on the cationic reverse flotation selectivity of iron oxides through a series of bench/micro flotation tests, zeta potential, powder contact angle, and Fourier Transform Infrared (FTIR), etc. The results pointed out that the use of recycled tailing water deteriorates the flotation selectivity and dilutes the concentrates. This can be largely attributed to the presence of Ca2+ ions at higher concentrations as they induce a drop in the Fe recovery and an increase in SiO2 content while an increase in the content of Mg2+ ions seems to have little effect on the quality of concentrate. As evidenced by the data from micro-flotation, powder contact angle, zeta potentials, and FTIR, a hydrophilic colloidal layer formed by Ca-based hydrolyzed compounds, such as Ca(OH)+ or, CaCO3(s), etc., on quartz could change its zeta potentials and disturb its interactions with a cationic collector. They also play a role in weakening the flocculation of starch on hematite probably by prelocking the acidic groups on the starch remnants and contracting their configurations, thus preventing their adsorption on mineral surfaces. However, magnesium ions seem to be beneficial to in strengthening the flocculation of starch on hematite as magnesium-based species could act as adsorption bridges of between starch and mineral surfaces.

3

Influences of process water chemistry on reverse flotation selectivity of iron oxides

Tang Min, Wang Dong, Wu Yan, Liu Dianwen

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 6

art. no. 151839

EN

It is critical for water quality in flotation as it dramatically influences the chemical/electrochemical properties of mineral surfaces and their interactions with reagents. Many potential variations could alter the water chemistry: water recirculation, mineral dissolutions, reagent additions, etc. This study aimed to identify the key elements from the recycled water sources affecting the separation efficiency in a typical industrial flotation circuit of iron oxides through a series of bench/micro flotation tests, zeta potential measurement, etc. The built-up and distribution of the dominant cations/anions in the process water from the roughers in the flotation system was also analyzed and recorded by Inductively Coupled Plasma-Optical Emission (ICP-OES) for a period of about three months when the operations were stable. The flotation results pointed out that a concentrate with a sharp increase of 6.0% Fe recovery and 2.5% SiO2 content was obtained by using the recycled tailing water only in comparison by using fresh water. In contrast, a slight uptrend in the grade of Fe but a substantial loss of near 6.5% Fe recovery occurs by using the treated sewage water alone instead. This could attribute to the ion distributions in these water sources, in which Ca2+, Fen+, Mg2+ or SO42ions were determined as the key ions influencing the flotation behaviors of the iron ore. But the competitive effects of Fe3+ ions were more significant than the ones of Ca2+ or Mg2+ ions. And the occurrence of starch could deteriorate the dilution of silicates in concentration induced by Fe3+/Fe2+ ions. It can be explained by zeta potential measurement or solution chemistry of those ions, indicating that at 8.5-9.0, the coating of the precipitates of Fe(OH)3(s) induced by iron ions alters a reverse on the zeta potentials of quartz. The presence of SO42-ions, however, has a positive role in reducing the possibility of slime coating on silicates due to acting as a chelating agent of iron ions.

4

Buffering of pulp pH and its influence on process water chemistry during iron ore flotation

Tang Min, Xiao Qingfei

Physicochemical Problems of Mineral Processing

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2021

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Vol. 57, iss. 4

157--167

EN

It is inevitable for the occurrences of pulp pH buffering during pH control in flotation as the minerals with acidic/alkali properties tend to interact with pH modifiers and restore the pulp pH. This could result in some disturbing ions and alter the water/pulp chemistry. The purpose of this study was to identify the influences of pulp pH buffering on process water chemistry through a series of pH buffering tests, bench flotation experiments, ore dissolution tests, zeta potential measurement, and Xray diffraction (XRD) analysis. The built-up and distribution of the dominant cations in the process water from different locations in an industrial flotation system of the iron ore were analyzed and recorded by Inductively Coupled Plasma-Optical Emission (ICP-OES) at a period of about six months when the operations were stable. The data showed that a near five-minute buffer of pulp pH at a range from near 7.9 to 8.9 occurred before it reached a stable value. At this period, the dissolution of Ca/Mg from the iron ore was dominant. And, the pulp pH at a lower value tended to induce more dissolved Ca2+ and Mg2+ ions. These divalent cations seem to have different influences on the flotation properties of iron oxides at the same concentrations, indicating a positive effect on the recovery of iron oxides with the presence of Mg2+ ions but an opposite effect if Ca2+ ions occurred. The presence of sulfate, however, tended to restore the floatability of silicate depressed by Ca2+ ions.