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• Acid treatment changed the surface properties of kaolinite and diaspore. • The principles of the surface property changes were analyzed by XPS. • Acid treatment affected flotation reagents (HMP and DAH) adsorption behavior. Kaolinite is one of the main associated minerals (gangue) in the processing of diasporic bauxites. Sulfuric acid pretreatment has been shown to have an improving effect on kaolinite-diaspore flotation separation, but the mechanism underpinning this effect is not well known. This study reports the surface chemistry of acid-treated kaolinite and diaspore in the presence of flotation reagents (sodium hexametaphosphate (SHMP) as a depressant and dodecylamine hydrochloride (DAH) as a collector) using X-ray photoelectron spectroscopy (XPS) analysis and zeta potential determinations. Quantitative XPS analysis revealed that the Al/Si atomic ratio on the kaolinite surface was reduced after the acid treatment. Compared with natural kaolinite, acid-treated kaolinite showed weakened adsorption properties for SHMP. Consequently, there was an enhanced DAH adsorption on the acid-treated kaolinite. High-resolution XPS analysis showed formations of "unsaturated Al" components on the diaspore surface after the acid treatment, which were ready to interact with phosphite groups of SHMP to depress diaspore in kaolinite flotation. Zeta potential studies also confirmed extended SHMP adsorption on acid-treated diaspore in comparison with the natural mineral. These findings form a firm knowledge for interpreting the application of kaolinite and diaspore in many adsorption studies, including the efficient separation between kaolinite and diaspore. [ABSTRACT FROM AUTHOR]

Highlights • Propyl gallate was introduced as a novel collector for diaspore flotation. • Propyl gallate exhibited excellent selectivity for diaspore against kaolinite. • Propyl gallate adsorbed onto diaspore surfaces through chemical bonding. Abstract Propyl gallate (propyl 3, 4, 5-trihydroxybenzoate; PG) was introduced as a new type of collector for diasporic bauxite flotation. The flotation performance of PG for diaspore and kaolinite was evaluated by comparing PG with sodium oleate (NaOl) as a typical collector through micro flotation tests. The results indicated that PG had higher collection ability for diaspore than for kaolinite at 15 mg/L and pH 7–9. Compared with NaOl, PG also exhibited higher selectivity for diaspore against kaolinite. Analyses of zeta potentials, adsorption amount, Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectra (XPS) revealed that PG adsorbed onto diaspore surfaces through chemical adsorption and hydrogen bonding, whereas PG hardly adsorbed onto kaolinite surfaces. Specifically, PG chelated with Al atoms on the diaspore surfaces by forming five-member rings through its ortho oxygens. These findings indicated that PG could be adopted as a novel collector for diaspore flotation and the activated phenolic hydroxyl groups also offered new insights for the development of flotation collectors. [ABSTRACT FROM AUTHOR]

The Bayer process is a conventional method for refining bauxite in the production of alumina. The Al/Si ratio in bauxite before feeding to the process must be enriched to more than eight by reducing impurities (mainly aluminosilicates). Therefore, diasporic bauxite ores (Al/Si < 6) have to be upgraded by pretreatment methods to meet the required quality for the Bayer process. Flotation separation (direct or reverse) followed by flocculation as an efficient pretreatment method is the main beneficiation technique for upgrading diaspore. Diaspore pretreatment by flotation favors several conditions and possesses certain limitations. This study has systematically explored various effective flotation factors (particle size, surface electrical charge, collectors, depressants, dispersants, flocculation and aggregation) and limitations in the pretreatment of diaspore and has compiled optimum results for its beneficiation. The summary offers various approaches for the selective flotation of diasporic ores via different conditions and suggests perspectives for further investigation. [ABSTRACT FROM AUTHOR]

The effect of temperature on the flotation behavior of sodium oleate on the surface of diaspore was investigated by using molecular dynamics (MD) simulations at three selected temperatures of 278.15 K, 303.15 K and 328.15 K. Conformational analysis, RDF analysis, hydrogen bonds statistics, SASA calculations and interaction energy analysis revealed that a certain range of temperature increase was beneficial for flotation, and the right temperature could yield better reagent dispersion and better mineral-reagent interactions. It was also noted that the enhanced molecular motion due to increased temperature may negatively affect the adsorption of the reagent on the mineral surface. The present study has theoretical implications for the effect of temperature on the flotation behavior of ionic surfactants on mineral surfaces. • The effect of temperature on flotation was studied by molecular dynamics. • Different temperatures showed different performances of sodium oleate in collecting diaspore. • A suitable temperature could make the sodium oleate better dispersed and distributed. • Higher temperature did not necessarily lead to a better flotation environment. [ABSTRACT FROM AUTHOR]

In this paper, a novel surfactant, 2-amino-6-decanamidohexanoic acid (AHA-10) was synthesized and used as a collector for flotation separation of diaspore and aluminosilicate minerals. The adsorption mechanism of AHA-10 onto diaspore was also evaluated by FTIR spectra, zeta potential, XPS and solution chemistry. The flotation results demonstrated that AHA-10 exhibited superior collecting power to diaspore and good selectivity against kaolinite and illite, and could effectively recover diaspore from bauxite ores contained aluminosilicate minerals at pH around 10. The analyses of FTIR spectra, zeta potential and solution chemistry inferred that at pH around 10, AHA-10 might chemisorb on diaspore surfaces by formation of Al O and Al N bonds. AHA-10’s unique properties, such as characteristic bond model to Al atoms on diaspore surfaces, double hydrophobic groups and intermolecular hydrogen bonds between neighboring AHA-10 molecules coated on diaspore surfaces, rendering a weakening surface energy and enhancing hydrophobicity of diaspore particles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Diaspore and kaolinite can transform into Na 2-x Al 2-x Si x O 4 by reacting with Na 2 CO 3. • The transformation is affected by temperature and the amount of Na 2 CO 3. • The leaching performance of Na 2-x Al 2-x Si x O 4 is negatively correlated with x value. A series of sodium aluminosilicates (Na 2-x Al 2-x Si x O 4 , x = 0.85, 0.55, 0.45, 0.35, 0.25 and 0.05) can be generated in the soda sintering process, some of which can be dissolved in sodium aluminate solution. This paper focuses on the transformation of aluminum-bearing minerals into Na 2-x Al 2-x Si x O 4 during the calcination of diasporic bauxite with different proportions of Na 2 CO 3 at 400–1100 °C. Based on thermodynamic analysis, the thermal behaviors, phase transformations and bonding changes of the aluminum-bearing minerals are investigated using thermogravimetric analysis and differential scanning calorimetric (TGA-DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) techniques. In addition, the dissolution performances of some Na 2-x Al 2-x Si x O 4 are verified by water leaching. The results demonstrate that the aluminum-bearing minerals in diasporic bauxite are diaspore and kaolinite, which are converted into Na 2-x Al 2-x Si x O 4 after calcination with Na 2 CO 3 at 700–1100 °C. Increasing the calcination temperature in the range of 700–1000 °C and the proportion of Na 2 CO 3 results in Na 2-x Al 2-x Si x O 4 having lower x value and decomposing into NaAlO 2 and Na 2 SiO 3 if Na 2 CO 3 is present in excess. As the mass ratio of bauxite to Na 2 CO 3 is 1, Na 1.95 Al 1.95 Si 0.05 O 4 is primarily formed at 900–1000 °C, which has excellent dissolution performance, close to that of NaAlO 2. Upon further increasing the calcination temperature to 1100 °C, Na 1.95 Al 1.95 Si 0.05 O 4 transforms into Na 2-x Al 2-x Si x O 4 with a higher x value, which has worse dissolution performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mixed NaOL/BHA exhibited better collecting ability and selectivity than NaOL. • NaOL and BHA co-adsorpted in diaspore surface. • BHA inhibited the chemisorption of NaOL on kaolinite. • Use of mixtures decreased bubble size and foamability & foam stability. In this paper, oleate sodium (NaOL) and benzohydroxamic acid (BHA) was introduced as a mixed collector for diaspore ores. The flotation behavior and the adsorption mechanism of mixed NaOL/BHA collector to diaspore and kaolinite was investigated by flotation tests, FTIR spectra analysis, zeta potential analysis, surface tension analysis and foam performance tests. The flotation results demonstrated that compared to NaOL, mixed NaOL/BHA collector exhibited superior collecting property and selectivity to diaspore against kaolinite. In detailed, the recovery of kaolinite reduced by 20.01% and the aluminum–silicon ratio (A/S) increased by 9.42 in micro-flotation tests; the total recovery rate was increased from 86.42% to 90.85%, and the A/S was increased from 10.68 to 15.27 in bench-scale flotation of a bauxite ore. The FTIR spectra and zeta potential analysis shows that BHA can promote the adsorption of NaOL on diaspore, and inhibit the adsorption of NaOL on kaolinite. The mixed NaOL/BHA collector not only has a significant effect on mineral selective adsorption, but also affects the surface activity of gas–liquid interface and flotation foam characteristics, thus affecting the flotation separation of these two minerals. The addition of BHA ensures that NaOL has good foaming properties and at the same time makes the foam less sticky, which can reduce the gangue minerals entrained in the foam product and is beneficial to the subsequent treatment of foam products such as filtration and dehydration. [ABSTRACT FROM AUTHOR]

The flotation and adsorption behaviors of two quaternary ammonium collectors DTAC (dodecyl trimethyl ammonium chloride) and CTAC (cetyltrimethyl ammonium chloride) on diaspore and kaolinite were investigated in this work. The flotation recovery of diaspore increases with the increase of pH and the decrease of particle size, however, the situations for kaolinite are opposite. Furthermore, the influence of pH on flotation of kaolinite decreases with the decrease of particle size, and for the fine particles (undersize 0.045mm), the flotation recovery with CTAC which has a longer hydrocarbon chain and is believed to have a stronger collecting ability is lower than that with DTAC. The dramatic differences of the flotation behaviors between diaspore and kaolinite are correlated to the differences of their crystal structures. The morphologies of diaspore and kaolinite particles in different size were studied by SEM. The kaolinite particles have much larger specific surface areas (about 7 times) than the diaspore particles due to their layered structure. This leads to the differences of collector adsorption behaviors on kaolinite and diaspore and results in the different flotation behavior. [ABSTRACT FROM AUTHOR]

Abstract: The existed collector for the flotation of diasporic bauxite in China is poor in selectivity. To look for a collector with high selectivity and strong collecting capacity on the diaspore flotation, novel 4-alkyl-4,4-bis(hydroxycarbamoyl) carboxylic acids (ABHC) including 4,4-bis(hydroxycarbamoyl) dodecanoic acid (HCDA), 4,4-bis(hydroxycarbamoyl) tetradecanoic acid (HCTA), and 4,4-bis(hydroxycarbamoyl) hexadecanoic acid (HCHA) were designed and synthesized for the beneficiation of diasporic bauxite by selective flotation. The results of flotation experiments for the single minerals showed that by using these compounds as collectors, the pulp pH value has significant influence on their collecting performance as the floatability of diaspore varies sharply with its change. The appropriate pH value for the flotation of diaspore gets close to neutral condition at which diaspore presents good floatability while kaolinite and illite exhibit poor floatabilities. HCDA, HCTA, and HCHA, especially HCDA, show good selectivity for the flotation between diaspore and aluminosilicate around pH 7. A satisfactory mass ratio of Al2O3 to SiO2 (A/S) and recovery of Al2O3 were obtained from the flotation separation of artificially mixed minerals and the flotation desilication of diasporic bauxite by using HCDA as a collector, proving that the selectivity of HCDA is better than that of the traditional collector oleate. Moreover, adsorption amount, zeta-potential, DFT calculation, XPS, and FTIR were performed to study the mechanisms. The results indicated that the adsorption of HCDA on the surface of diaspore is dominantly chemisorption in the form of three chelate rings. The oxygen atoms contained in carboxyl and hydroxycarbamoyl of the polar group have the highly negative charges and stereo conditions to form five- to eight-membered ring, resulting in the coordination of carboxyl and hydroxycarbamoyl to the metal aluminum atoms to form chelate rings. By contrast, the adsorption of HCDA on the surface of kaolinite or illite is mainly physical adsorption. [Copyright &y& Elsevier]

Abstract: The flotation behaviors of kaolinite and diaspore were investigated using N,N-dipropyl dodecyl amine (PN). Maximum recoveries of kaolinite and diaspore were about 90% and 50%, respectively. Both recoveries of kaolinite and diaspore increased with the increasing dosage of PN. On the basis of the zeta potential and FT-IR spectra, the ionization of surface hydroxyl and the isomorphic exchange of surface ions account for the charging mechanisms of surfaces of kaolinite and diaspore. The adsorption mechanism of PN on the surface of two minerals was mainly electrostatic. After reacting with PN, the zeta potential of kaolinite and diaspore both increased, and comparing with the original zeta potentials, potential of kaolinite increased much more than that of diaspore, this can explain why recovery of kaolinite is higher than that of diaspore. [Copyright &y& Elsevier]

Abstract: Highly branched waxy maize starch (WMS) was used to separate diaspore from artificial mixtures of diaspore and kaolinite by microflotation using dodecylamine (DDA) as collector. It was found that WMS depressed the diaspore flotation while activated the kaolinite flotation more or less. The adsorption of WMS on diaspore was examined through adsorption test, zeta potential measurement, infrared spectroscopy, and atomic force microscopy. It is suggested that both chemical interaction and intermolecular hydrogen bonding by hydroxyl groups of starch with surface Al–OH moieties occurred in the adsorption. Results obtained from the adsorption of DDA and WMS on diaspore showed that starch virtually enhanced the DDA adsorption. The depressant action of WMS can be rationalized primarily by the formation of hydrophilic adsorption layer enveloping the surface of diaspore and covering the collector. [ABSTRACT FROM AUTHOR]

Abstract: Hydrolyzate of hogwash oil (HHO) was prepared at ambient pressure using hogwash oil that was collected from the dietary industry as a raw material by means of non-pressurized multistage hydrolyzation. Before hydrolyzation, the collected hogwash oil was subject to pre-treatment that included deposition edulcoration, acidification degumming and deodorization by digestion as well as vacuum dewatering. Components of the synthesized products were detected by gas chromatography and the results indicated that unsaturated fatty acids are the major components. Using HHO as a collector, the flotation behavior of diaspore and kaolinite was investigated. The reaction mechanisms of diaspore and kaolinite with HHO are discussed based on a zeta potential test. The results showed that a concentrate with a mass ratio of Al2O3 to SiO2 of 14.42 and an Al2O3 recovery of 81.80% can be obtained at a feed mass ratio of Al2O3 to SiO2 of 5. This indicated that the HHO is a potential collector for separating diaspore from aluminosilicate minerals in bauxite. The results also suggested a possible way to reuse discarded hogwash oil to avoid environmental pollution. [Copyright &y& Elsevier]

Abstract: A new environmentally friendly design for low-grade diasporic-bauxite processing which is different from the Bayer and sintering processes was proposed in this paper. In the redesign of alumina production technology, a mixture of bauxite ore and sodium hydroxide solution was heated at a higher temperature for the purpose of complete decomposition of bauxite. The products were then extracted by water; the resulting sodium aluminate solution was further purified and used for the gibbsite precipitation, the residue being reacted with a caustic liquor to recover sodium oxide and alumina. The experimental results show that during the new process bauxite decomposition rates approach 100% and the residues can be easily recovered. When diasporic ores with mass ratio of alumina to silica of approximately 5:1 are treated, total alumina recovery efficiency of 86% and a sodium oxide presence below 1.5% in the final red mud will be achieved. This new design surpasses previous approaches in terms of high resource efficiency and low environmental impact. [Copyright &y& Elsevier]

Abstract: The utilization of a non-toxic natural polysaccharide, soluble starch, in the flotation of diaspore and kaolinite with emphasis on depression of diaspore in the reverse flotation of bauxite ores by using a Gemini cationic collector, is reported in this work. Firstly, the depressant effect of soluble starch was studied by pure mineral micro-flotation of diaspore and kaolinite as functions of the depressant dosage and pulp pH. The results show that soluble starch depresses diaspore much better than kaolinite. When pH is over 10, a satisfactory separation of the alumina and the silicate minerals can be approached. Moreover, micro-flotation tests of artificial mixed minerals and bench scale reverse flotation of the diasporic bauxite ore was complementing conducted. The non-charged starch is highly proved to be an effective and selective depressant for the reverse flotation of diaspore from the gangue minerals like kaolinite. By zeta potential measurement, adsorption studies and D-IR spectra analysis, the mechanism of interaction between starch and the diaspore surfaces is established, which is the formation of a five membered ring complexes on mineral substrates. The number of broken Al–O bonds of diaspore is much more than that of kaolinite, so the selectivity separation of diaspore from kaolinite in this system is feasible. [Copyright &y& Elsevier]

Abstract: The effect of cationic groups on performance of 12-carbon chain collectors in flotation separation of diaspore from kaolinite, pyrophyllite and illite has been investigated by flotation tests and explained by density functional computations. The flotation test results indicated that the separation of diaspore from these aluminosilicate minerals was feasible at strong alkaline conditions by using cationic collectors, dodecylamine chloride (DDAC), dodecyl trimethyl ammonium chloride (DTAC) or dodecylguanidine sulfate (DDGS), respectively. In strong alkaline conditions, these three collectors showed excellent selectivity against diaspore, however, DDGS returned superior collecting ability for aluminosilicate minerals compared with DDAC and DTAC. By using the density functional theory (DFT), we calculated some properties such as the H and N atomic charges and cationic group charges which are related to the reactive behavior of 12-carbon chain collectors at B3LYP/6-31G (D) level. The results of calculations indicated that the efficiencies of these three cationic collectors depend on the investigated parameters, and DDGS is better than DDAC and DTAC as a collector agent. The theoretically obtained results are consistent with the flotation tests. [Copyright &y& Elsevier]

Abstract: Beneficiation of a diasporic-bauxite ore by selective flocculation with sodium polyacrylate (PAS) was studied. Flocculation behaviors of diaspore, kaolinite, illite and pyrophyllite in the presence of PAS were also investigated by sedimentation tests. PAS shows good selectivity for the flocculation separation of diaspore from silicates in the range of pH 8–12. A concentrate with Al2O3/SiO2 ratio 8.9 and the recovery of Al2O3 87.0% was obtained from a diasporic-bauxite ore with Al2O3/SiO2 ratio 5.7 with the addition of sodium carbonate 5kg/t and PAS 7g/t. Micro-photogram, zeta potential and FTIR measurements were then performed to study the mechanisms. It was observed that the zeta potentials of diaspore shifted to negative value strongly and the isoelectric point (IEP) of diaspore was also changed from about pH 6–4, and the flocs of diaspore were larger and denser than that of kaolinite in the presence of PAS. A new band at 1640cm−1 was found in the infrared spectrum of the diaspore after interaction with PAS, and this new band matched the characteristic peak at 1624cm−1 in the infrared spectrum of the reaction products of PAS and AlCl3. The adsorption of PAS on diaspore is concluded to be chemisorption caused by the chemical reaction between carboxylate group and the exposed Al sites on diaspore surface. [Copyright &y& Elsevier]

Abstract: Novel carboxyl hydroxamic acids compounds, including 2-carboxyl-6-methylcyclohexane carboxamic acid (CMCA), 2-carboxymethyl-decylen-4-yl hydroxamic acid (CDHA), and 2-carboxymethyl-tetradecen-4-yl hydroxamic acid (CTHA) were synthesized, and the flotation behaviors of diaspore, kaolinite and illite were investigated by using these compounds as collectors. The adsorption mechanism of CTHA on the surface of diaspore, kaolinite and illite was conducted by zeta-potential, adsorption amount and FTIR spectra measurement. The interaction of CTHA on the diaspore surface may be mainly dominated by the chemical adsorption; however, the adsorption of CTHA on kaolinite or illite is mainly dominated by the physical one. [ABSTRACT FROM AUTHOR]

• Revealing the effect of water quality on the flotation of low-grade diasporic bauxite. • Different cations show different effect on surfactant adsorption on mineral surface. • Synchrotron NEXAFS is pioneered to investigate the speciation change of surfactant adsorption on mineral surface. Froth flotation has been proved to be the economic way to upgrade the low-grade diasporic bauxites by desilication of kaolinite. However, the recovery rate of diaspore varied significantly in industry due to water quality (cations) and the mechanism remains unknown. This report investigates the effect of common water hardness cations (Ca2+ and Mg2+) on the recovery of diaspore and kaolinite using micro-flotation at various pH values. The results show that adding Ca2+ significantly enhanced the diaspore recovery rate even under acidic conditions (pH = 4–7). In contrast, adding Mg2+ reduced the diaspore recovery rate to below 50% when the pH value was between 8 and 9 while adding Ca2+ increase the recovery rate to above 95%. In addition, adding either cation shows minimal change to the recovery of kaolinite. The mechanism has been revealed by thermodynamics speciation, zeta potential and synchrotron-based near edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The change of both dipole-dipole interaction and hydrogen bonding plays a vital role on this cation effect. [ABSTRACT FROM AUTHOR]