Serpentine Particles Research Articles

Effects of biodegradable dispersants on the separation flotation of chalcopyrite and serpentine

The presence of serpentine slime coating on the chalcopyrite surfaces severely affects the chalcopyrite floatability. In this study, three biodegradable polymers, namely polyaspartic acid (PASP), polyepoxy succinic acid (PESA), and hydrolyzed polymaleic (HPMA) were used as dispersants to disperse the chalcopyrite and serpentine particles. The micro-flotation experiments demonstrated that the application of dispersants in the flotation effectively reduced the negative impact of serpentine over a wide pH range, restoring the recovery rate of chalcopyrite to about 85%. The XPS analysis revealed that the dispersants could be adsorbed onto the mineral surfaces through the binding of carboxyl groups with the magnesium or copper sites. As a result, the surface potentials of serpentine changed from positive to negative, while that of the chalcopyrite became even more negative, resulting in a strong electrostatic repulsion between them, which effectively eliminated the covering of the serpentine on the chalcopyrite surface. The AFM force measurements indicate a weak interaction of the polycarboxylic acids dispersants with the surface of chalcopyrite. Consequently, the adsorption of dispersants on the chalcopyrite surface has an insignificant impact on the subsequent adsorption of collectors, which is further supported by the adhesion force measurements between the air bubble and mineral surfaces. Therefore, the application of polycarboxylic acid dispersants in the flotation significantly enhanced the floatability of chalcopyrite in the presence of the serpentine fines.

Modulating particle-particle interaction in phyllosilicate serpentine aqueous suspensions using sodium citrate

The depletion of high-grade nickel sulfide ores has led to an increased interest in low-grade ultramafic ores, which are widely available but challenging to process due to their high content of phyllosilicate serpentine. The anisotropic surface charge and shape of serpentine particles lead to attractive interactions, which increase the viscosity of ore slurry and associated operational and equipment costs. To overcome this challenge, we investigate the application of an environmentally benign reagent, sodium citrate, to modify the particle-particle interactions in serpentine aqueous suspensions. Our results show that at alkaline pH (10), sodium citrate selectively adsorbs on the brucite plane of serpentine, making the entire particle overall negatively charged, which weakens the interparticle attraction and reduces the suspension's shear viscosity, yield stress, and storage modulus. We confirmed these results using colloidal probe atomic force microscopy (AFM) technique, which showed a significant weakening of attraction between silica and brucite surfaces upon the addition of citrate. This work enhances the understanding of surface interaction mechanisms of phyllosilicate serpentine particles in aqueous media with the addition of sodium citrate and provides useful implications for the application of green reagents in mineral operations involving phyllosilicate gangues. Our findings suggest that sodium citrate has great potential as an effective and sustainable reagent in the processing of abundantly available low grade ultramafic nickel ores.

The effects of ultrasonic wave on heterogeneous coagulation and flotation separation of pentlandite-serpentine

It is well known that in the flotation of copper-nickel sulfide ore, pentlandite and serpentine are easy to form hetero-aggregation, which makes it difficult to separate them. Therefore, dispersion operation is indispensable, including chemical and physical dispersion. Chemical dispersion is usually achieved by adding dispersing reagents, which is widely used in mineral flotation, while the study of ultrasonic dispersion in copper-nickel sulfide ores in physical dispersion is less reported. Thus ultrasonic dispersion technology was introduced to weaken the hetero-aggregation and to improve the floatability of pentlandite. Through the implementation of a series of conditional tests of influence factors including ultrasonic site, ultrasonic probe type, ultrasonic time, and ultrasonic power, the optimum ultrasonic dispersion system was demined, and the results showed that the ultrasonic power was the key factor affecting the dispersion of pentlandite-serpentine. Then the dispersion mechanism of ultrasonic was revealed by means of supernatant turbidity measurements, particle-size distribution (PSD) analyses, scanning electron microscopy (SEM), and atomic force microscope (AFM) in succession. Coupled with supernatant turbidity measurements, PSD analyses and SEM images of flotation concentrates all confirmed that the ultra-fine serpentine particles coating on the coarse pentlandite particles were effectively dispersed. AFM analyses depicted the morphological changes of surface roughness treated by different ultrasonic power, and confirmed that the ultrasonic power of 200 W could increase the surface roughness and floatability of pentlandite but decrease that of serpentine. Thus, the difference in floatability between the two minerals were enlarged so as to achieve efficient separation of the two minerals. The results of this research are helpful to understand clearly the mechanism of ultrasonic dispersion of pentlandite-serpentine, which provides an alternative dispersion technology and exhibits great potential for further study and application.

Preparation and application of sustainable nanofluid lubricant from waste soybean oil and waste serpentine for green intermittent machining process

A great amount of waste cooking oil (WCO) and waste serpentine arise in daily life or industrial production. Serpentine is a type of hydrated magnesiumsilicate often employed as flux material for steel industry. Recycling of WCO and waste serpentine is of great significance to the solution of environmental issues and the promotion of economy. On the other hand, machining process has great impacts on global economy. Large amounts of mineral oil-based lubricant are consumed by the machining process, causing many health and environmental problems. Thus, this work studied preparation and application of sustainable nanofluid lubricant from waste soybean oil (WSO) and waste serpentine for green intermittent machining process. WSO hydrolysis and free fatty acids esterification were used to acquire modified WSO (MWSO). Epoxidized soybean oil (ESO) and MWSO constituted the base oil. The base oil was adjusted by changing the volume ratio VR of ESO to MWSO. Serpentine nanoparticles were obtained by mechanically reducing the size of waste serpentine particles. The volume fraction Vp of nanoparticles in the lubricant was set to have different values. Bioinspired hexagonal recessed microstructure was fabricated on tool surface for performance enhancement of the lubricant. The results revealed that the parameter combination of VR = 50% and Vp = 2.1% resulted in the optimum friction performance and cutting performance at relatively low cost. This work offered a new solution to the sustainable nanofluid lubricant used in green intermittent machining process. Moreover, the proposed solution provided new economic opportunity.

A comparison study between bioflocculants and PAM for dewatering of ultrafine phyllosilicate clay minerals

Several environmental problems have been reported when synthetic organic and inorganic flocculants are used to treat fluid fine tailings (FFT), especially phyllosilicate clay minerals, generated in the mining plants. These hazardous issues have increased the importance of using natural flocculants from renewable sources (biopolymers). This investigation has explored the impact of proteins (protamine and lysozyme) and polysaccharides (chitosan, pectin, lignin, and alginic acid) as natural flocculants and compared their results in the same conditions by using Polyacrylamide (PAM) as a traditional organic polymer. Ultrafine kaolinite and serpentine particles (−10 μm) were chosen as the challenging gangue minerals for chalcopyrite copper ore (CuFeS2) and pentlandite nickel ore ((Fe, Ni)9S8)), respectively. Capillary suction timer (CST) and filtration tests were considered for comparative assessments. Assessments indicated that PAM in shear rate ~ 20 (1/s) has a viscosity ~90 times higher than the examined biopolymers. This high viscosity limited PAM distribution as a flocculant through the suspensions. Results highlighted that PAM had the highest flocculation activity in low dosages (0.05 and 0.1 wt%) while in dosages above 0.25 wt%, cationic biopolymers; protamine, and lysozyme for kaolinite and anionic pectin for serpentine showed a higher performance than the other polymers. The addition of Ca2+ could increase the dewatering of the clay minerals and promote the flocculation strength of the biopolymers. Generally, results indicated that the flocculation function of protamine and lysozyme (cationic proteins) at the optimum dosage (0.5 wt%) was higher than other tested biopolymers, while pectin (an anionic polysaccharide) improved the dewatering of serpentine particles. Outcomes of this study proved that commercially available bioflocculants have a significant potential to use in the treatment of FFTs and decrease environmental problems that occur by using inorganic and organic flocculants.

New perceptions into the detrimental influences of serpentine on Cu-Ni sulfide flotation through rheology studies and improved the separation by applying garnet

The flotation separation between sulfides and fine serpentine has always been a difficult problem due to their hetero-coagulation. To acquire a better understanding on the adverse effect of fine serpentine on Cu-Ni sulfide flotation, rheology measurements and flotation tests on Cu-Ni sulfide/serpentine system were explored under different conditions in this study. Rheology results revealed that in the aqueous solution at pH 9.5–10, serpentine particles could partially aggregate in pulp, whereas Cu-Ni sulfide particles did not aggregate. In the mixed Cu-Ni sulfide/serpentine system, the higher the total solid concentration was, the greater the influence of serpentine proportion on pulp rheology was. When pulp solid concentration was higher than 10 %, pulp viscosity increased obviously as serpentine proportion increased no matter in the absence or presence of potassium butyl xanthate (PBX). However, with the increase of serpentine proportion, pulp yield stress gradually increased in aqueous solution, indicating the hetero-coagulation between sulfide and serpentine occurred, while in the presence of PBX, the pulp yield stress increased first and then decreased. The deterioration of the flotation performance of Cu-Ni sulfide suggested that the hetero-coagulation was not the only factor affecting the flotation of Cu-Ni sulfide containing serpentine, high pulp viscosity could also worsen that. However, with the addition of coarse garnet particles (-104 + 44 μm), the pulp yield stress decreased remarkably, illustrating that the hetero-coagulation between sulfide and serpentine was limited. Furthermore, pulp viscosity also decreased obviously, and the synthetic actions improved Cu-Ni sulfide flotation. Micro-flotation and batch flotation results verified that the Ni recovery in concentrate increased significantly with a remarkable decrease in SiO2 content after adding garnet (-104 + 44 μm). This study offered some new insights into the adverse effect of serpentine on sulfide flotation, and the employment of stir medium such as garnet, might be a potential way to improve the flotation separation of sulfides from serpentine.

The flotation separation of galena and pyrite using serpentine as depressant

Toxic inorganic depressants are commonly used in the flotation separation of polymetallic sulfide ores and it is desirable that they can be replaced by environmentally benign substances. Serpentine, a common gangue mineral encountered in complex sulfide ores, has been found to be an efficient depressant for ferric sulfide (e.g., pyrite). Serpentine was tested as a potential selective depressant in the differential flotation separation of galena and pyrite using potassium butyl xanthate (PBX) as a collector. In single mineral flotation, serpentine depressed the −150 + 74 μm and −74 + 37 μm galena while the −10 μm galena was floatable. Different from galena, serpentine has strong depression effect on all the three sizes of pyrite. So the flotation separation of fine grained galena and pyrite can be achieved. A concentrate with Pb grade of 65.09% and recovery of 67.72% can be achieved in the mixed minerals flotation when serpentine was added as depressant. Mechanism studies indicated that serpentine particles attach to the surface of pyrite more easily.

Insights into the dissolution kinetics of thermally activated serpentine for CO2 sequestration

The rate-determining step in the aqueous carbonation of serpentine minerals is the dissolution of Mg from serpentine. The dissolution rate of minerals largely depends on the pH of the solution and the size of serpentine particles. In the present work, an experimental method has been developed to study the dissolution rate of heat activated serpentine (lizardite polymorph) in a wide range of pH, solid to liquid ratio and particle size at room temperature. The results allowed us to determine the effect of these variables on the dissolution kinetics of heat activated lizardite, which represents crucial kinetic data for accurately modelling the carbonation rates of serpentinite. Additionally, amorphous Si re-precipitation at high solid to liquid (S/L) ratio and pH 6.1 was demonstrated. These provide essential data for the design and optimisation of industrial mineral carbonation processes. For the first time, the crackling core model (CCM) was applied to model the dissolution kinetics of heat activated lizardite in acidic solutions. Applying the CCM model to a wide range of particle sizes provides useful information on the mechanism of the dissolution of heat activated lizardite and the range of particle size for which the assumptions of the model are valid. Characterising serpentine particles leached under different conditions, along with analysing model parameters, provided a new insight into the mechanism of the dissolution of heat activated lizardite.

A Two-step CO2 Mineralization Process

This communication briefly highlights our preliminary work on building a lab-scale, two-step CO2 mineralization process plant. Thermally activated serpentine was dissolved in one reactor to release Mg2+ ions without the use of any additive. CO2 from a flue gas (10 mol% CO2 in N2) was transformed into pure synthetic hydromagnesite at 90°C under ambient pressure conditions in a second reactor. A novel design for a solid dosing system was developed that allows for continuous feeding of activated serpentine particles. The operation under ambient pressure conditions, however, was found to be problematic with regards to liquid circulation between the reactors. Nevertheless, the experience from this work has allowed us to design a more robust experimental set-up for CO2 mineralization.

The effect of graphene oxide on the slime coatings of serpentine in the flotation of pentlandite

This paper studied the effects of graphene oxide (GO) on the slime coatings of serpentine in the flotation of pentlandite. The flotation results showed that the flotation recovery of pentlandite was improved with the addition of GO, compared with carboxymethyl cellulose (CMC). The possible mechanisms of the improved flotation recovery were investigated by electrokinetic study, FTIR study, sedimentation tests and scanning electronic microscopy (SEM) analysis. The experimental results demonstrated that both of the two depressants dispersed the hydrophilic serpentine particles from the pentlandite surface. For GO, however, the flocculation of serpentine was a further reason responsible for the enhanced recovery of pentlandite.

Talc and serpentine particles morphology effect upon their distribution in flotation products (through the example of the Pechenga copper-nickel ores)

Talc and serpentine particles morphology effect upon their distribution in flotation products (through the example of the Pechenga copper-nickel ores)

Accelerating Natural CO2 Mineralization in a Fluidized Bed

The presence of water (H2O) is essential for the adsorption of carbon dioxide (CO2) on the serpentine particles. However, the use of H2O in the slurry bed columns requires high energy inputs to maintain the temperature during operation above ambient temperatures. Moreover, the separation, drying, handling, and processing of the product stream will pose challenges and cost even more energy. Here, we show the proof of principle of CO2 sequestration on mineral particles in a fluidized bed using a moist CO2 stream. The setup allows wetting of the particles while maintaining fluidization. The results show 50% mineral conversion and 40% CO2 conversion in 8 min at 1 bar and 90 °C.

Tribological behaviours of surface-modified serpentine powder as lubricant additive

Purpose – The aim of this paper is to study the tribological performance and self-repairing performance of surface-modified nanoscale serpentine powders as lubricant additives in the mineral base oil (5-CST). Design/methodology/approach – Fourier transform infrared spectroscopy spectra and thermo-gravimetric analysis of both modified and unmodified serpentine were performed to analyse their grafting ratio and suspension after modified using a long-chain naphthene aliphatic acid. The tribological properties of surface-modified serpentine as lubricant additives in 5-CST were evaluated and the worn surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Findings – The results show that the serpentine particles have high grafting ratio, improving the dispersity in 5-CST. When the serpentine concentration of 1.00 weight per cent is used as additives in 5-CST, friction coefficient reduces by 14.80 per cent under 294 N and wear scar diameter (WSD) decreases by 11.82 per cent. The results of X-ray absorption near edge structure and XANES show that the adsorption and tribochemical reactions occur to form self-repairing lubrication films. Originality/value – The paper illustrates a tribofilm form on the rubbed surface, which is responsible for the decrease in friction and wear, mainly containing iron oxides, silicon oxides, magnesium oxides and organic compounds. The results are useful for further applications in advanced environmental friendly lubricating oils and additives.

Reactivity of Callovo-Oxfordian Claystone and its Clay Fraction With Metallic Iron: Role of Non-Clay Minerals in the Interaction Mechanism

AbstractIn order to better understand the possible interactions between steel canisters and a claystone host rock, in this case the Callovo-Oxfordian rock (COx), the present study investigated in detail, under conditions relevant to high-level radioactive waste repositories (anoxic conditions, temperature of 90°C), the reactions between metallic iron and: (1) COx; (2) the clay fraction extracted from COx (CF); and (3) mixtures of CF with quartz, calcite, or pyrite. Batch experiments were then carried out in the presence of NaCl-CaCl2 background electrolyte, for durations of 1, 3, and 9 months. Solid and liquid end-products were characterized by a combination of techniques including liquid analyses, transmission and scanning electron microscopies, X-ray diffraction, N2 adsorption at 77 K, and Mössbauer spectroscopy. The interaction between CF and metallic iron appeared to proceed by means of pathways similar to those illustrated in previous studies on interactions between metallic iron and purified clays. In spite of the many similarities with previous studies, significant differences were observed between the behavior of COx and CF, particularly in terms of pH and Eh evolution, iron consumption, chemical composition of the neoformed particles, and textural evolution. Such differences demonstrate the important role played by non-clay minerals in reaction pathways. The addition of carbonates or pyrite to CF did not lead to significant change in reactivity. In contrast, under the conditions used in the present study, i.e. for relatively low iron:clay ratios, the presence of quartz strongly influenced reaction pathways. In the presence of quartz, magnetite was observed only in trace abundances whereas the amounts of magnetite were significant in experiments without quartz. Furthermore, filamentous serpentine particles with a small Al:Si ratio appeared which could develop from an FeSiAl gel that only forms in the presence of quartz. Considering that most clay rocks currently being considered for radioactive waste disposal contain significant amounts of quartz, the results obtained in the present study may be of significant interest for predicting the long-term behavior of clay barriers in such sites.

An amorphous Si[sbnd]O film tribo-induced by natural hydrosilicate powders on ferrous surface

The tribological properties of surface-coated serpentine powders suspended in oil were evaluated using an Optimal SRV-IV oscillating friction and wear tester. The worn surface and the tribo-induced protective film were characterized by scanning electron microscope and focused ion beam (SEM/FIB) work station, energy dispersive spectroscopy (EDS) and transmission electron microscope (TEM). Results indicate that with 0.5wt% addition of serpentine powders to oil, the friction coefficient and wear rate significantly decrease referenced to those of the base oil alone. An amorphous SiOx film with amorphous SiOx particles inserted has formed on the worn surface undergoing the interactions between serpentine particles and friction surfaces. The protective film with excellent lubricating ability and mechanical properties is responsible for the reduced friction and wear.

Characterization of Tribofilms Generated from Serpentine and Commercial Oil Using X-ray Absorption Spectroscopy

The chemical and tribological properties of serpentine particles suspended in lubricating oil were investigated using a pin-on-disk high frequency friction machine at 100 °C. The wear scar width of the upper steel pins was measured by an optical microscope. The tribofilm was characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) elemental mapping, and X-ray absorption near-edge structure (XANES) spectroscopy. It was found that the addition of serpentine to commercial engine oil improves its tribological properties. The SEM and EDX elemental mapping shows that a tribofilm formed by the commercial oil with serpentine contains silicon, magnesium, oxygen, phosphorus, sulfur, zinc, calcium, and carbon on the worn surface, which is different from the tribofilm formed by the commercial oil without serpentine. The results of the XANES analysis show that the addition of serpentine to the commercial oil changes the chemical compositions of the tribofilms. This change may account for the better tribological properties of the lubricating oil containing serpentine. The formation mechanism of the tribofilm is discussed.

Aqueous Ammonia Capture Integrated With ex-Situ Mineralisation Using Recyclable Salts for Industrial CCS

Carbon dioxide capture and storage by mineralization (CCSM), also known as ex-situ mineralization, is an important technology for industrial CCS. The feedstocks for CCSM can not only be Mg/Ca-silicate minerals, but can also include waste materials from industries, such as steel slags and waste cement. Aqueous ammonia capture is preferred for industrial CCS, since industrial emissions present high CO2 concentrations (around 25 vol.%) and more impurities (SO2/NOx) than that from power plants. Aqueous ammonia CO2 capture integrated with ex-situ mineralisation avoids stripping CO2 as pure gas from absorbents and compression of CO2, and therefore reduces the high energy consumption of capture. In this study, optimization experiments were conducted on this process. The dissolution efficiency of Mg from serpentine using 2.8M NH4HSO4 at 100g/l solid to liquid ratio for 1h was around 80%. The decrease in dissolution efficiencies is because of the Si passive layer on the surface of serpentine particles. The molar ratio of Mg: NH4+ salts: NH3 is the key factor controlling carbonation efficiency, and when using the molar ratio of Mg: NH4+ salts: NH3 is 1:1.5:2, the carbonation efficiency was 96%.

Tribochemical aspects of interactions between high-dispersed serpentine particles and metal friction surface

The paper presents the results of experimental investigations of friction-induced chemical modification of steel in the presence of serpentine additives in the lubricating material. This process is accompanied by substitution of magnesium atoms of the mineral structure by iron atoms from the friction surface. As a result, recombination of the crystalline lattice of the initial mineral and the formation of pseudo-mineral structures similar to the plane SiO compounds occur.

Tribological properties of serpentine, La(OH)3 and their composite particles as lubricant additives

La(OH)3 nanoparticles and serpentine/La(OH)3 composite particles were synthesized via sol–gel method. The phase compositions, micro-morphology of the synthesized particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tribological properties of different samples were tested and compared by the MM-10W Multi-functional friction abrasion tester and MHK-500 Ring-block wear testing machine. The TEM figure indicates that La(OH)3 nanoparticles are granular, the average size of the particles is 50nm. The SEM figure of the composite particles illustrates that La(OH)3 particles uniformly coat on the surface of serpentine particles. The results of the friction tests indicate that serpentine, La(OH)3 and serpentine/La(OH)3 composite particles all exhibit friction-reducing and anti-wear properties compared to the base oil. The oil containing the composite particles have the best friction-reducing, anti-wear and self-repairing properties. The friction coefficients are reduced by 24.63% and the diameters of friction spots are reduced by 41.88% compared to the base oil. The energy spectrum of tribosurface gives evidence of that the contact area of rubbing pair was repaired by composite particles during friction tests.

Research on Tribological Properties of Serpentine Particles as Lubricating Oil Additives

This paper adopts wet method to prepare serpentine particles on the planetary ball mill, executes lipophilic degree tests and friction and wear tests of these particles. The results showed that: 1) as the modification agent, the optimum dosage of oleic acid is when the volume ratio of oleic acid and serpentine particles is 2, and the optimum time of milling (modification) is 24h. 2) 4012 maritime lubricating oil with serpentine particles has obvious anti-wear and friction effect, and the optimum dosage range of serpentine particles is 0.9%-1.0%. According to the outcomes of metallurgical microscope observation and electron microprobe analysis, a conclusion can be drawn: during the process of friction and wear, serpentine particles brought on physical or chemical reactions with the surface of test samples, create a layer of protective film, thus this kind of lubricating oil has filling function to the furrow of friction pair surface, so as to decrease the surface roughness, decrease the degree of friction and wear.