Characterization of halloysite from Morocco: evaluation of its suitability for ceramic industry

peer reviewedaudience: researcher, professional, student, popularization, otherHalloysite from Nador (NE Morocco) has been studied to evaluate their suitability in ceramic industry. Cross-section involving all the Messinian facies was performed in the Melilla Neogene basin, at the foot of the Gourougou volcano, in order to understand the origin of the halloysite and appreciate its reserves. White layers of halloysite and red clays rich in smectite occurred in contact with basal reef limestone, were characterized by mineralogical (XRD, IR), textural (SEM) and physico-chemical analyzes (grain-size, Atterberg limits, ATD/TG, XRF and specific surface area). Ceramic proprieties were evaluated for fired halloysite from 500 to 1100°C in order to appreciate technical processing for ceramic production. The halloysite consists of fine particles with a high plasticity and a large specific surface area. XRD results revealed the presence of 7Å non-hydrated halloysite with the presence of gibbsite, alunite, K-feldspar plus other minor phases, and traces of smectite and illite. Infrared spectroscopy confirms the occurrence of characteristic bands of halloysite at 3695 and 3618 cm-1. SEM observations confirmed the predominance of tubular facies typical of halloysite. The chemical analysis revealed high aluminum content linked to the presence of some aluminous phases (gibbsite and alunite). ATD/TG and XRD results of fired clay sample evidenced halloysite dehydroxylation and a rearrangement of metakaolinite to form mullite and spinel from 975°C. Moroccan halloysite has good properties for refractory ceramic application. However, quartz sand addition is required to avoid any cracks development at firing as well as to reduce the plastic behaviour of raw halloysite and minimize shrinkage during sintering