RESEARCH ARTICLE Determination of point of zero charge of natural organic materials Elisee Nsimba Bakatula 1,2 & Dominique Richard 1,2 & Carmen Mihaela Neculita 3 & Gerald J. Zagury 1,2 Received: 20 May 2017 /Accepted: 20 December 2017 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract This study evaluates different methods to determine points of zero charge (PZCs) on five organic materials, namely maple sawdust, wood ash, peat moss, compost, and brown algae, used for the passive treatment of contaminated neutral drainage effluents. The PZC provides important information about metal sorption mechanisms. Three methods were used: (1) the salt addition method, measuring the PZC; (2) the zeta potential method, measuring the isoelectric point (IEP); (3) the ion adsorption method, measuring the point of zero net charge (PZNC). Natural kaolinite and synthetic goethite were also tested with both the salt addition and the ion adsorption methods in order to validate experimental protocols. Results obtained from the salt addition method in 0.05 M NaNO 3 were the following: 4.72 ± 0.06 (maple sawdust), 9.50 ± 0.07 (wood ash), 3.42 ± 0.03 (peat moss), 7.68 ± 0.01 (green compost), and 6.06 ± 0.11 (brown algae). Both the ion adsorption and the zeta potential methods failed to give points of zero charge for these substrates. The PZC of kaolinite (3.01 ± 0.03) was similar to the PZNC (2.9–3.4) and fell within the range of values reported in the literature (2.7–4.1). As for the goethite, the PZC (10.9 ± 0.05) was slightly higher than the PZNC (9.0–9.4). The salt addition method has been found appropriate and convenient to determine the PZC of natural organic substrates. Keywords Point of zero charge . Point of zero net charge . Isoelectric point . Salt addition method . Ion adsorption method . Cation exchange capacity . Zeta potential . Organic materials Introduction A promising approach to treat the low concentrations of ele- ments (Sb, As, Cd, Cr, Co, Mn, Hg, Mo, Ni, Se, and Zn) found in contaminated neutral drainage (CND) is to design a passive reactor where metal sorption onto low-cost materials consti- tutes the main treatment mechanism. The substrates for these reactors can originate from industrial wastes or natural sources, but they must be locally available to ensure cost ef- fectiveness. To treat various types of effluents, different substrates are selected based on their surface properties and their sorption capacities. In the neutral pH range, depending on their surface functional groups, some substrates might per- form better in the presence of anions while others are more suited for the capture of cations. Natural and organic sub- strates possess functional groups such as carboxyl, sulfhydryl, hydroxyl, and amino groups, responsible, by their ionization, for the negative and positive charges on their surface. The magnitude of the surface charge depends on the abundance and types of functional groups present, and on the pH of the solution (Mukherjee et al. 2011). Points of zero charge (PZCs) are pH values at which the surface charge components become equal to 0 under given conditions of temperature, applied pressure, and aqueous so- lution composition (Sposito 2008). This does not mean that the surface has no charge at pH PZC , but rather that there are equal amounts of positive and negative charges. PZC values could help optimize the selection of a substrate for the treat- ment of a CND. Substrates with low PZC values would be best suited to treat effluents contaminated with cations, while substrates with high PZC values would be more appropriate to capture anions. Responsible editor: Philippe Garrigues * Gerald J. Zagury gerald.zagury@polymtl.ca 1 RIME-Research Institute on Mines and Environment, Montréal, Canada 2 Department of Civil, Geological, and Mining Engineering-École Polytechnique de Montréal, Montréal, QC H3C 3A7, Canada 3 RIME-Université du Québec en Abitibi-Témiscamingue, Rouyn-Noranda, QC J9X 5E4, Canada Environmental Science and Pollution Research https://doi.org/10.1007/s11356-017-1115-7