Exploring the Influence of Milling Parameters on the Wet Mechanochemical Synthesis of Mg-Al Layered Double Hydroxides

The synthesis of Mg-Al layered double hydroxide was explored, through a one-step wet mechanochemical route, using a NETZSCH LME 1 horizontal bead mill. Raw materials selected were MgO and Al(OH)3. The aim of the research was to expand on the understanding of the wet mechanochemical synthesis of Mg-Al LDH. This was done through variation in milling parameters such as rotational speed, retention time, solids loading, bead size and jacket water inlet temperature. LDH synthesis occurred successfully at jacket water temperatures of 50°C and increased retention times. LDH XRD peaks were noted to be broad, but the pattern evident. It was further noted that Al(OH)3 XRD peak reduction occurred readily for increased rotational speeds and residence times, regardless of system temperature. MgO reacted more readily at elevated temperatures.

X-Ray Fluorescence
Samples were dried at 100°C and roasted at 1000°C to determine the mass loss upon ignition. Additionally, 1 g of sample was mixed with 6 g of Lithium tetraborate flux and fused at 1050°C to form a stable glass bead. Analysis was conducted with the use of a Thermo Fischer ARL Perform ‘X Sequential instrument. Samples were characterised using UNIQUANT software.

Particle Size Analysis (PSA)
Collected samples were analysed wet, to ensure full dispersion using a Mastersizer 3000 with Hydro LV liquid unit.

XRD Analysis
Powdered samples were analysed using a PANalytical X’Pert Pro powder diffrac-tometer in θ-θconfiguration, fitted with an X’Celerator detector and variable divergence- and fixed receiving slits. The set-up made use of a Fe filtered Co-Kα (λ= 1.789 Å) source. Sample preparation was conducted using a standardised PANalytical backloading system which provides a random particle dis-tribution. Samples were scanned from 5°to 90°with a step size of 0.008°. Mineralogy was determined using the ICSD database in correlation with X’Pert Highscore plus software

FT-IR spectra for dry samples were obtained with the use of a PerkinElmer 100 Spectrophotometer over a range of 550 – 4000 cm-1. An average of 32 scans at a resolution of 2 cm-1 was used.

Sample morphology was investigated by making use of a Zeiss Gemini 1 cross beam 540 FEG SEM. Powdered samples were coated with graphite 5 times using a Polaron Equipment E5400 SEM auto-coating sputter system.

S1: 1 h, 30 deg C, 1000 rpm, 10 % Solids
S2: 1 h, 30 deg C, 2000 rpm, 10 % Solids
S3: 1 h, 30 deg C, 3000 rpm, 10 % Solids
S4: 1 h, 30 deg C, 2000 rpm, 10 % Solids
S5: 2 h, 30 deg C, 2000 rpm, 10 % Solids
S6: 3 h, 30 deg C, 2000 rpm, 10 % Solids
S7: 1 h, 30 deg C, 2000 rpm, 20 % Solids
S8: 1 h, 30 deg C, 2000 rpm, 30 % Solids
S9: 1 h, 30 deg C, 2000 rpm, 10 % Solids, 0.25 mm
S10: 1 h, 50 deg C, 2000 rpm, 10 % Solids
S11: 2 h, 50 deg C, 2000 rpm, 10 % Solids
S12: 3 h, 50 deg C, 2000 rpm, 10 % Solids
S13: 1 h, 50 deg C, 2000 rpm, 10 % Solids
S14: 1 h, 50 deg C, 1000 rpm, 10 % Solids
S15: 1 h, 50 deg C, 3000 rpm, 10 % Solids