Research report Fluoride 54(3):269-282 July-September 2021 Fluoride removal from aqueous solution by almond shell activated carbon Akbari, Balarak, Yousefi, Rigi, Mahvi 1 1 [Now published in full after the initial publication as an Epub ahead of print on July 11, 2021 at www.fluorideresearch.online/epub/files/131.pdf] FLUORIDE REMOVAL FROM AQUEOUS SOLUTION BY ALMOND SHELL ACTIVATED CARBON Hamideh Akbari, a Davood Balarak, b Maseoud Yousefi, a Parisa Rigi, c Amir Hossein Mahvi d,e, * Tehran, Shiraz, and Zahedan, Iran ABSTRACT: Fluoride (F - ), the ion of the element fluorine, is one of the mineral elements present in nature that enters drinking water through underground aquifers and when present in high concentration it can lead to risks such as skeletal, dental, and non- skeletal fluorosis with morbidity such as decreased IQ and negative effects on brain development, tooth discolouration, and bone pain. The aim of the study, was to study the ability of activated carbon developed from almond shell (ACAS), to remove fluoride from an aqueous solution. We examined the effects on fluoride removal efficiency of contact time, initial F - concentration, pH, and ACAS mass. The equilibrium data were also examined with models including the Langmuir, Freundlich, and Temkin isotherms. The removal characteristics were validated through the use of different kinetic models for the estimation of the solute interaction and the nature of the biosorption. A contact time of 60 min, an adsorbent dosage of 0.6 g/L, and a pH of 3 were considered to be the optimal operational conditions. The biosorption of F - onto ACAS and the equilibrium data follow from the Langmuir adsorption isotherm with a maximum adsorption of 84.3 mg/g and a regression coefficient of R 2 =0.999. The kinetic studies showed that the system fitted the pseudo-second order kinetic model. Thus, this work gives new insights on the interaction of ACAS with F - in a reconstituted aqueous solution. Keywords: Activated carbon; Almond shell; Fluoride; Kinetics; Isotherms. INTRODUCTION: The sources of fluorine in water and soil are mostly geogenic and include several rock forming minerals. 1-4 The load of the fluoride ion (F - ) in water is also increased by various industries, such as those producing pesticides, ceramics, refrigerants, and aerosol propellants, Teflon cookware, and glassware. 5,6 Fluoride is considered to be able to prevent dental caries by decreasing the rate of demineralization of dental enamel and reversing the progression of existing decay by promoting the rate of remineralization. 7-9 Various values have been given for the permissible limit for the fluoride concentration in potable water with the World Health Organization (WHO) recommending a desirable upper limit of fluoride in drinking water of 1.5 mg/L. 10-12 However, countries can set their own country standards and lower standards have been set of 0.6 mg/L in Senegal, West Africa, and 1 mg/L in India with a rider to the Indian limit of “the lesser the fluoride the better, as fluoride is injurious to health.” In 2015, in the United States of America, a recommendation was made for community water systems that practice fluoridation of 0.7 mg/L, a reduction from the previous recommendation of 0.7–1.2 mg/L. 13 a Department of Environmental Health Engineering, Mamasani Education Complex for Health, Shiraz University of Medical Sciences, Shiraz, Iran; b Health Promotion Research Centre and Department of Environmental Health Engineering, School of Public Health, Zahedan University of Medical Sciences, Zahedan, Iran; c Student Research Committee Zahedan University of Medical Sciences, School of Public Health, Department of Environmental Health Engineering, Zahedan, Iran; d Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran; e Center for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran; For correspondence: Associate Professor Amir Hossein Mahvi, Center for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran; E-mail: ahmahvi@yahoo.com