Many works concern the increase in the contact of surface of carbonates of various origins, by means of their chemica 26, thermal 27 or mechanical modification 28. Therefore, most studies use carbonates of biological origin: shells of chicken eggs, or shells of clams or snails 21, 22, 23, 24, 25. Calcium carbonate of geological origin has low efficiency in heavy metal adsorption 20, and the main removal mechanism is the exchange reaction with the formation, as mentioned, of poorly soluble metal compounds. Numerous studies describe the mechanisms that are prevalent in the process of removal of heavy metals from solutions depending on the nature of carbonates, which can be seen in the different structure of materials 17, 18, 19. For this purpose, mineral calcium carbonate and its biological forms, e.g. The processes of biosorption have also been intensified by means of various types of modifications, for example preparation of biosorbent mixtures 15 or by methods requiring conversion of biomass into biochar 16.Īnother way of removing heavy metals from solutions is to create poorly soluble metal compounds in the form of hydroxides or carbonates. For removal of heavy metals from aqueous solutions, among others, cellulose 6, saw dust 7, 8, bark 9, straw 10, nut shells 11, 12 cereal bran 13, 14 and other materials are used. Large amounts of waste biomass with good sorption properties are provided for instance by agriculture, forestry and the agri-food industry. It is believed that the removal of metal cations from waters by means of biomass is a cheap process and is characterized by high efficiency 4, 5.
3, and for several decades research has also focused on the possibilities of using biosorbents, often constituting waste products. In order to remove heavy metal cations from water, many conventional treatment techniques are used, such as chemical precipitation, ion exchange, electrochemical treatment, membrane technologies, adsorption, etc.
In this aspect, an important element of water quality protection is the elimination of threats at source-even during the stage of wastewater generation. Also, the presence of other anthropogenic elements is recorded in the Arctic waters, as exemplified by the results of tests on the presence of heavy metals accumulated in narwhal organisms 2. It has been found, for instance, that one of the sources of Pb and Hg origin in Svalbard is a sea aerosol 1. Global water pollution is evidenced by the increasing level of pollution in the Arctic waters. Untreated wastewater discharge leads to an increasing level of pollution of the seas and oceans, which is also caused by contaminated rainwater and drainage from fields. Surface water pollution, including heavy metals, is a serious environmental problem of global importance. It has been shown that an important role in the process of heterophasic ion exchange is played by neutralization of protons-desorbed from the biosorbents-with hydroxide ions released into the solution by partial dissolution of CaCO 3 and subsequent hydrolysis reaction.
It was found that under the conditions of the experiment, the addition of powdered CaCO 3, in a weight ratio of 1 g CaCO 3: 15 g BS, increases the removal efficiency of all the metals studied by 20–30%. A synergy effect in the flow system was also investigated. For the removal of lead cations, a measurable effect is found only for biosorbents whose active centers are saturated with protons (improvement in removal efficiency by about 20%). Removal efficiency for Cu and Zn has been shown to increase from 20 to 50% depending on the BS used. Studies conducted under static conditions have shown that the effect of Cu and Zn cations removal from solutions is better when using a mixture of BS and CaCO 3 as compared to the effect of process, in which these two components were used separately. The main mechanism of biosorption of heavy metal cations is ion exchange, whereas the reaction with calcium carbonate results in precipitation of poorly soluble carbonates and hydroxides of the examined heavy metals. The effect of calcium carbonate on the removal efficiency of cations of the selected heavy metals Cu, Zn and Pb from aqueous solutions using various biosorbents (BS) was investigated under laboratory static conditions.
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