Wet Comminution Research Articles

Abrasion-Induced Acceleration of Melt Crystallisation of Wet Comminuted Polybutylene Terephthalate (PBT).

Within this contribution, the effect of grinding media wear on the melt crystallisation of polybutylene terephthalate (PBT) is addressed. PBT was wet ground in a stirred media mill in ethanol using different grinding media beads (silica, chrome steel, cerium-stabilised and yttrium-stabilised zirconia) at comparable stress energies with the intention to use the obtained particles as feed materials for the production of feedstocks for laser powder bed fusion additive manufacturing (PBF-AM). In PBF-AM, the feedstock’s optical, rheological and especially thermal properties—including melt crystallisation kinetics—strongly influence the processability and properties of the manufactured parts. The influence of process parameters and used grinding media during wet comminution on the optical properties, crystal structure, molar mass distribution, inorganic content (wear) and thermal properties of the obtained powders is discussed. A grinding media-dependent acceleration of the melt crystallisation could be attributed to wear particles serving as nuclei for heterogeneous crystallisation. Yttrium-stabilised zirconia grinding beads proved to be the most suitable for the production of polymer powders for the PBF process in terms of (fast) comminution kinetics, unchanged optical properties and the least accelerated crystallisation kinetics.

A novel approach for modelling of physical interactions between slurry, grinding media and mill structure in wet stirred media mills

Wet comminution is an important process in the mineral processing industry. Modelling of wet comminution in stirred media mills requires the simultaneous modelling of grinding media, a moving internal stirrer, and slurry. In the present study, a novel approach for modelling the physical interactions between slurry, grinding media and mill structure in a stirred media mill is presented. The slurry is modelled with the particle finite element method (PFEM). The grinding media is modelled using the discrete element method (DEM) and the mill structure is modelled using the finite element method (FEM). The interactions between slurry, grinding media and mill structure are modelled by two-way couplings between the PFEM, the DEM and the FEM models. The coupled model of the present study is used to predict the motion of slurry and grinding media, and to calculate the power draw during wet comminution in a pilot scale horizontal stirred media mill. Furthermore, the model is used to compare a Newtonian and a non-Newtonian model of the slurry, where the non-Newtonian model is used to capture experimentally observed shear-thinning. The coupled PFEM-DEM-FEM model preserves the robustness and efficiency of each of the methods and it gives the possibility to use large time increments for the fluid, greatly reducing the computational expense. The coupled model of the present work provide information on the complex dynamics of slurry and grinding media. The numerical model is shown to be a useful tool for increasing the knowledge and understanding of wet comminution in stirred media mills.

Effects of Pretreatment on the Yield of Peanut Oil and Protein Extracted by Aqueous Enzymatic Extraction and the Characteristics of the Emulsion.

Effects of comminution on peanut particle size and yield of peanut oil and protein were analyzed. Additionally, the emulsion properties (surface protein concentration, particle size, and ξ-potential) were compared. Moreover, different demulsification methods were used to investigate the emulsion stability. Results showed that the yield of peanut oil and protein was highest (87.23% and 82.05%, respectively) after dry comminution for 72 s. Upon wet comminution for 120 s, the yields of peanut oil and protein were 89.91% and 84.70%, respectively, which were both significantly higher than that obtained after dry comminution (p < 0.05). The surface protein concentration and ξ-potential of emulsion made by dry comminution (DCE) were 7.02 mg/m2 and 12.08 mV, respectively, and those of emulsion made by wet comminution (WCE) were 10.71 mg/m2 and 15.25 mV, respectively, which were significantly higher than that of DCE (p < 0.05). The volume average particle size of DCE was 3.41 µm, which was significantly higher than that of WCE (3.18 µm, p < 0.05). Collectively, these results indicated that WCE was more stable than DCE. Further, the demulsification rate of DCE was significantly higher than that of WCE when treated by freeze-thawing, pH, papain, and phospholipase A2 (p < 0.05). Demulsification effect of Alcalase 2.4L was the best among these five demulsification methods treated, and the demulsification rate of DCE reached 92.77%, which was slightly higher than that of WCE (92.67%), further illustrating the higher stability of WCE.

Guidelines to adjust particle size distributions by wet comminution of a bioactive glass determined by Taguchi and multivariate analysis

A quaternary bioactive glass of high silica content was used as a model system for flexible design of powder characteristics obtained by ball milling. The dependence on milling time was used to demonstrate consistency with the expected correlation between comminution and cumulative kinetic energy of impacting balls. Additional experiments were based on Taguchi planning of simultaneous changes in milling time, balls-to-powder ratio and ethanol-to-powder ratio, with ethanol used as a process control agent (PCA) to prevent agglomeration and to seek greater flexibility in the design of powder distributions. Plausible physical mechanisms allowed us to obtain improved fitting by multivariate analysis, based on log-log scales. Normal distribution was found to be well-suited to describe the actual particle size distributions, which are very positively skewed. Weibull distributions provided good fitting, mainly by considering the three different contributions from particles in small, medium and large size ranges. These contributions are affected differently by ball milling parameters, as demonstrated by finer analysis. This yields suitable conditions for a flexible design of asymmetric powder size distributions (i.e. bimodal or skewed), in addition to a decrease in average particle size - both highly significant factors when designing glass-ceramic powders for robocasting and additive manufacturing.

Research in the Field of Preparing Molded and Unmolded Refractories Based on High-Alumina HCBS. Part 9. Preparation and Properties of Mixed HCBS Composition: Fuzed Bauxite-Corundum, Quartz Glass, Reactive Alumina. Dilatometric Study of Materials Based on Them

Combined wet comminution is used to prepare HCBS of composite composition, including fuzed bauxite-corundum as a basic material (89%) and very fine fuzed quartz (11%). Specimens are also based on this HCBS with an increased Al2O3 content due to introducing 10 – 30% reactive alumina into their composition. Dilatometric studies are performed making it possible to establish that for materials of all compositions there are four typical nonisothermal heating temperature ranges: normal thermal expansion (up to 900°C), sintering or shrinkage (900 – 1300°C), mullitization or growth (1300 – 1450°C), and sintering (shrinkage) of mullitized material (1450 – 1500°C).

Mechanochemical aspects in wet stirred media milling

Wet comminution in stirred media mills is a frequently applied fully scalable top-down method towards the production of micron- and submicron particles. Despite the vast field of mechanochemistry which encompasses an increase in reactivity due to the effect of mechanical energy input, there is still no clear picture of the involved mechanisms. In ultra-fine wet grinding the situation is further complicated due to the presence of the solvent: reactions of the stressed solid with the surrounding liquid phase can occur. In this paper several aspects of mechanochemistry occurring in stirred media mills are outlined through suitable experiments. Main focus lies on the comprehensive product characterization and on the role of the liquid phase. It is shown that the liquid phase influences product properties like particle size, porosity, particle shape, structure, chemical composition and the molecular termination of the surface. An increase in the reactivity of ground solids is manifested by a significant increase in dissolution in the aqueous phase during processing in water. Altogether, the liquid dispersion medium which can act as solvent is thus introduced as a new process parameter in stirred media milling and offers new prospects for innovative product design by top-down approaches.

RECOVERY OF METALS FROM ZINC-CARBON AND ALKALINE SPENT BATTERIES BY USING AUTOMOTIVE SHREDDER RESIDUES

ABSTRACT The main aim of this work is the thermal recovery of manganese and zinc from a mixture of zinc-carbon and alkaline spent batteries containing 40.9% of Mn and 30.1% of Zn after a pre-liminary physical treatment followed by the removal of mercury. Separation of the metals is car-ried out on the basis of their different phase change temperatures, in fact the boiling point of mercury and zinc are 357 °C and 906 °C, respectively, and the melting point of Mn 3 O 4 , the main Mn-bearing phase in the mixture, is 1564 °C. After wet comminution and sieving to remove the anodic collectors and most of the chlorides contained in the mixture, chemical and X-ray powder diffraction (XRPD) analyses were per-formed. The mixture was initially heated in an air flow at temperatures ranging from 300 °C to 400 °C to eliminate mercury, then, the flow of air was turned into an inert carbon dioxide at-mosphere. The volatilization of metallic zinc starts at a temperature 850 °C. At higher temperature the reduction of zinc oxide and subsequent volatilization of metallic zinc is carried out by the carbon present in the original mixture or in the automotive shredder residue (car fluff) added from the outside. By optimization of temperature, stoichiometric ratio and residence time, a product suit-able for production of new batteries after refining was obtained. The treatment residue consist-ed of manganese and iron oxides that could be used to produce manganese-iron alloys.

Top-down Processing of Submicron 45S5 Bioglass® for Enhanced in Vitro Bioactivity and Biocompatibility

45S5 Bioglass® (45S5BG - 45wt.% SiO2, 24.5wt.% CaO, 24.5wt.% Na2O and 6wt.% P2O5 glass forming system) is a frequently applied type A bioactive material, forming an inherent bond to bone and soft tissue. Recent studies for nanometer sized bioactive glasses (nBG) have indicated their great potential for several biomedical applications. It is recognized that cost-efficient processing routes are required for the development of submicron bioactive glasses, given the advantages associated with the nanoscale. In this study, the potential of top-down processing of 45S5BG by wet comminution in a stirred media mill is investigated and the key importance of the used solvents is revealed: whereas bioactive submicron particles can be produced in organic solvents, as shown exemplarily for n-pentanol, bioactivity is lost after processing in water. Analysis of the elemental constituents in the solid phase by ICP-OES indicates enhanced dissolution during processing in water, i.e. the glass composition is changing during processing. In n-pentanol the overall composition and structure is maintained and only the formation of surface carbonates is observed; flake-like particles are obtained. As a marker for bioactivity in vitro hydroxycarbonate apatite formation as determined by FTIR is used; biocompatibility is addressed by in vitro incubation with osteoblast like MG-63 cells. All-together, we propose wet comminution under controlled conditions as an appropriate technique to produce submicrometer bioactive glass particles with enhanced bioactivity.

A NEW THERMAL PROCESS FOR THE RECOVERY OF METALS FROM ZINC-CARBON AND ALKALINE SPENT BATTERIES

The aim of this study is the thermal recovery of manganese and zinc from a mixture of zinc-carbon and alkaline spent batteries containing 40.9% of Mn and 30.1% of Zn after a preliminary physical treatment. Separation of the metals is carried out on the basis of their different phase change temperatures, the boiling point of zinc being 906°C and 1564°C that of Mn3O4, the main Mn-bearing phase in the mixture. After wet comminution and sieving to remove the anodic collectors and most of the chlorides contained in the mixture, chemical and X-Ray Powder Diffraction (XRPD) analyses were performed. The mixture was heated in CO2 atmosphere and the temperature raised, thus permitting the zinc oxide to be reduced to metallic zinc by the carbon present in the original mixture. Other tests were carried out by addition to the mixture of activated charcoal (95% C) or of the automotive shredder residue (fluff) containing 45% C.A zinc product was obtained suitable, after refining, for the production of new batteries. The treatment residue consisted of manganese and iron oxides that could be used to produce manganese-iron alloys. From these results, an integrated process for the recovery of the two metals was proposed.

A NEW THERMAL PROCESS FOR THE RECOVERY OF METALS FROM ZINC-CARBON AND ALKALINE SPENT BATTERIES

The aim of this study is the thermal recovery of manganese and zinc from a mixture of zinc-carbon and alkaline spent batteries containing 40.9% of Mn and 30.1% of Zn after a preliminary physical treatment. Separation of the metals is carried out on the basis of their different phase change temperatures, the boiling point of zinc being 906°C and 1564°C that of Mn3O4, the main Mn-bearing phase in the mixture. After wet comminution and sieving to remove the anodic collectors and most of the chlorides contained in the mixture, chemical and X-Ray Powder Diffraction (XRPD) analyses were performed. The mixture was heated in CO2 atmosphere and the temperature raised, thus permitting the zinc oxide to be reduced to metallic zinc by the carbon present in the original mixture. Other tests were carried out by addition to the mixture of activated charcoal (95% C) or of the automotive shredder residue (fluff) containing 45% C.A zinc product was obtained suitable, after refining, for the production of new batteries. The treatment residue consisted of manganese and iron oxides that could be used to produce manganese-iron alloys. From these results, an integrated process for the recovery of the two metals was proposed.

Enhancing In Vitro Bioactivity of Melt‐Derived 45S5 Bioglass® by Comminution in a Stirred Media Mill

45S5 Bioglass® (45S5 BG) is a frequently applied Type A bioactive material, capable of forming an inherent bond to bone and soft tissue. Currently, applied melt‐derived bioactive glass powders (BG) exhibit particle sizes between a few to several hundred micrometers. Recent studies on nanometer‐sized bioactive glasses (nBGs), produced by bottom‐up methods like sol–gel processing or flame spray pyrolysis, have indicated their great potential for several biomedical applications. In this study, the feasibility of top‐down processing starting from bulk 45S5 BG by wet comminution in a stirred media mill was investigated. The products were assessed by in vitro hydroxycarbonate apatite (HCAp) formation in simulated body fluid, which is a marker for bioactive behavior. The study reveals the paramount influence of the used solvent for a successful top‐down processing: In comparison with the as‐received material bioactivity is lost for powders processed in water, preserved for comminution in ethanol and increased for powders processed using the alcohols n‐butanol, n‐pentanol, and n‐hexanol. It was also found that only for the latter solvents, the chemical composition of the glass is maintained during comminution. Flake‐like, slightly porous particles with specific surface areas of ~25–30 m2/g are obtained. Thus, the presented comminution approach offers a convenient technique to process 45S5 BG with enhanced bioactivity.

Study on Wet Treatment Process of Waste Printed Circuit Boards

The dry crushing of wasted printed circuit boards (PCBs) can make secondary contamination. In this paper, a wet comminution process is put forward to solve the difficulties. For the comminution product, the distributions of particle size, liberation degree and metal grade are analyzed, and for the product below 1mm, a wet metal beneficiation process combined with shaking table and flotation is employed. The results show that the Whole PCBs could be comminuted by the MX wet impact crusher, and the cumulative yield, liberation degree, total metal content and its copper grade of the product below 1mm is 83.49%, 97%, 83.46% and 20.50%respectively, and that metal concentrates could be beneficiated by XZY wet shaking table, and the yield, total metal weight, copper grade of the metal concentrate, the recovery of total metal and copper is 34.87%, 88.99%, 50.73%,79.90% and 78.07% respectively keeping the feeding concentration at 20% and water consumption in 1100L/h. For these metals included by shaking-table middling, the separation of both flotation and shaking table is carried out, and the total metal content and its copper grade, recovery in metal concentrate 2′ is 72.07% , 31.59% and62.04% respectively, meanwhile the copper grade of tailings in flotation and shaking table are decreased to 1.26% and 2.94%. The wet treatment process can effectively concentrate these valuable metals from waste PCBs.

Folate-targeted drug-delivery systems prepared by nano-comminution

Background: The size reduction ability of conventional wet comminution has been improved by proper polymeric stabilizer systems, and the resulting nano-comminution methods have led to the commercialization of many poorly water-soluble drugs after improving their bioavailability. During nano-comminution, polymer steric stabilizers physically adsorb onto the surface of drug particles. Method: In this study, the cross-linking and subsequent functionalization methods of the physically adsorbed polymers were used to widen the applicability of the nano-comminution. Chitosan was used as a steric stabilizer for two hydrophobic drugs, naproxen and paclitaxel. Results: Chitosan was successfully cross-linked (immobilized) by tripolyphosphate. The cross-linked stable polymer layer on drug nanoparticles was conjugated with folic acid, a model targeting moiety. The chemical reactions were performed without destroying the stabilities of drug nanosuspensions. The cross-linking and conjugation reactions significantly modified the release profiles of drug nanoparticles. Conclusion: This simple preparation method can be utilized to prepare novel drug encapsulations and folate-targeted delivery systems.

Wet comminution kinetics of dolomite at laboratory scale

Wet comminution tests of discretized dolomite sample were conducted in planetary ball mill and reported in this work. The effect of ball diameter and feed size on the comminution kinetics was investigated. Literature models were used in attempt to provide adequate selection function estimation. Rajamani and Herbst model was proposed for evaluation of the selection functions ( S j ) in planetary ball mill under given process conditions. Model parameters were correlated to ball diameters. The methodology suggested in this paper can provide assessment of model parameters and consequently S j parameters. This work represents a good foundation for further quantification of interactions in the comminution processes, and thus the prediction possibility of product properties in various process units and process conditions.

Suspension rheology during wet comminution in planetary ball mill

Obtaining and controlling desirable system behavior in terms of rheology is important issue in many engineering problems. This study monitors rheological behavior of dolomite suspensions produced by wet comminution in planetary ball mill. Dolomite has a number of uses, in agriculture, steel making, glass making, ceramic industry, pharmaceutical industry, etc. Therefore, it is very interesting for investigation. Rheological behavior of attained suspensions was characterized as strongly pseudoplastic whereas the pseudoplasticity degree was connected to particle size distribution. Rheological properties of the product become equal after the effective comminution time regardless of primary particle properties before comminution. Therefore, the comminution in a highly energetic mill such as planetary ball mill, within short time interval will induce development of systems with the same granulometric and consequently the same rheological properties regardless of the primary system properties before the comminution.

Wet comminution of raw salt using high-pressure fluid jet technology

Based on the impact mechanism and fluid wedge effect of the high-pressure fluid jet, a new approach to raw salt comminution has been worked out. The fluid jet comminution process has a unique characteristic of providing a fine appearance for the product particle as well as a high washing efficiency. Dissolution of raw salt and loss of product are avoided owing to saturated sodium chloride solution used as high-pressure medium. Compared with mechanical comminution, the product processed by this technique has higher quality and better appearance. The working condition is also improved since the comminution is operated under wet conditions. Also, this approach has the potential to be used to comminute the thermally sensitive, inflammable and explosive materials.

Amphiphilic amino acid copolymers as stabilizers for the preparation of nanocrystal dispersion

The recent advance of particle size engineering in nanometer ranges has widened the formulation opportunities of relatively water-insoluble drugs. However, the ‘nanoformulation’ suffers from a lack of systematic understanding about the requirements of polymeric stabilizers. Furthermore, the polymers that can be used for the preparation of nanocrystals are so limited that finding a proper stabilizer for a given formulation is often difficult. In this study, amino acid copolymers whose properties can systematically be tailored are developed, and their morphological and compositional effects are investigated. Copolymers containing lysine (K) as their hydrophilic segments, and phenylalanine (F) or leucine (L) as their hydrophobic segments successfully produce stable nanocrystals (200–300 nm) in water, while copolymers of K and alanine (A) could not generate nanosized particles. Not the morphology but the hydrophobicity of copolymers seems to be a critical parameter in the preparation of drug nanocrystals by wet comminution. The effective stabilization performance of copolymers requires the hydrophobic moiety content to be higher than 15 mol%. Comminution for only 5 min is long enough for nanocrystal preparation, and the crystallinity of drug is found intact after the processing.

Role of polymeric stabilizers for drug nanocrystal dispersions

Nanoparticle engineering of drug crystals is an important basic tool for efficient and intelligent drug delivery. Recently, the wet comminution process of drug nanocrystals in the presence of polymeric stabilizers has been successfully developed, but it has not been well understood yet how to select a proper stabilizer for a drug. In this study, the nature of interactions between polymeric stabilizers and drugs was investigated by analyzing the steady state particle sizes of 7 drugs obtained by wet comminution. The surface energy of drugs and polymers measured by contact angle measurement was found to be an important factor, although it could not solely determine the steady state values of particle size. In addition to surface energy, specific interactions between functional groups appeared to play a certain role. The stabilization ability of polymers and the subsequent steady state particle size of drug nanocrystals depend on various parameters including surface energy and specific interactions.

Durable Nanocrystalline PSZ For SOFCs and Sensors

High temperature SOFCs and sensors need electrolyte materials with high mechanical strength and thermal shock resistance for secure assembly and reliable service. These materials can be produced economically from commercial coprecipitated hydroxide powders using a special pretreatment, including heating and wet comminution to prevent mixing of stabilizing agents. Sintered ceramic bodies show high fracture toughness and strength, and the toughness-to-strength ratio becomes much higher. Such mechanical behavior ensures the ultimate in thermal shock resistance as well as mechanical and thermal endurance.

Cross piston press for high pressure comminution of fine brittle materials

The cross piston press possesses four hydraulic cylinders mounted crosslike. Each of them acts on one piston of the working block in the center. The oppositely orientated pistons are activated simultaneously and the both piston pairs act alternatively. In this way a multiple crosswise stressing of the material in the working chamber of the block is achieved. The cross piston press can comminute a fine material to a microfine powder. Locked-cycle experiments were done with limestone, quartz and smelted corundum, and a product fineness was achieved of x 95=3–4 μm. The specific energy consumptions were 60 kW h/t with limestone, 300 kW h/t with quartz, and 480 kW h/t with corundum, these values are remarkable less then those ones of milling in stirred mills. Considerations on the throughput lead to the results that industrial units could have a capacity up to 4000 kg/h (limestone), 1500 kg/h (quartz), and 400 kg/h (corundum). The test device was designed for a dry operation, however it is possible after some modifications to perform a wet comminution with a high concentrated slurry. A cross piston press might also be employable for mechanical activation.