The growing demand for mineral resources followed by the steady increase in mining activity result in the need for the disposal of a large amount of tailings. Environmental impacts of mining have been studied and reported by several investigators [
1,
2,
3,
4]. In particular, the potential harmful impact of waste disposal on the environmental quality of the surrounding ecosystem is attracting an increasing amount of focus, which has led to stricter environmental regulations. Hence, the global mining industry has realized that the initiatives should address the concept of sustainable development.
Submarine tailings placements (STPs) is a viable option to land-based waste disposal and has been utilized at several mineral processing plants around the world [
4,
5,
6]. The potential environmental impacts of STPs are the results of the oceanographic, biochemical, and ecological conditions of the site, as well as the specific mineral processing solution employed by the plant. The physiochemical properties of the tailings are governed by the preceding comminution and separation processes, but there is considerable potential for improving these characteristics through novel approaches to dewatering and flocculation, as well as the recycling of process water and process chemicals. These are established unit operations, but they are not necessarily studied and optimized for the reactions that take place in a system where tailings are disposed to the marine environment and fresh process water meets seawater.
Currently, legislation has spurred the industry to continuously replace reagents with more environmentally friendly alternatives. In Norway the esterquats-containing reagent FLOT 2015 is now being used as a more environmentally friendly cationic collector for reverse flotation of silicates in the production of high-purity, micronized calcite slurries. Esterquats constitute a novel class of cationic collectors with the ester bond located between the quaternary ammonium group and the long hydrocarbon chain, and can be decomposed into non-surface-active and more environmentally friendly components [
7,
8,
9]. When FLOT 2015 molecules bound to a silicate mineral surface via physical adsorption are exposed to seawater with its much higher ionic strength, significant desorption can occur. Furthermore, the fast hydrolysis of the esterquats collector can be initiated in seawater.
A recent review of the literature on this topic [
10] found that the primary step in the degradation of esterquats is probably an abiotic degradation via chemical reactions such as oxidation, reduction, and hydrolysis without the participation of biological organisms. The important decomposition reaction is the hydrolysis in the presence of water. Therefore, the degradation starts with the cleavage of the ester bond. Overkempe et al. [
9] highlights that the hydrolytic stability of esterquats is influenced by the temperature, pH, formulation pathways, and the chemical structure of the molecule. In general, basic medium hydrolysis gives rise to the formation of fatty acids and small diol/triol quaternary ammonium salts [
11]. Although, detailed biochemical studies are not available for all esterquat types, a general explanation of the degradation pathway of esterquats were made based on research with radiolabeled chemicals. Giolando et al. [
12] reported that the results from high-performance liquid chromatography (HPLC) with radiometric detection showed the disappearance of dimethyl bis(2-(1-oxooctadecyl)oxyethyl) ammonium chloride (DEEDMAC) in the solution followed by the presence of a fatty acid and a short-chain quaternary ammonium compound. The fatty acids and the short-chain quaternary ammonium compounds are readily biodegradable into inorganic end product such as water, carbon dioxide, and mineral salts [
11,
13,
14,
15,
16]. Furthermore, photochemical reactions have to be taken into account as one of the main pathway of biodegradation of chemicals [
17]. While the oxidative photodegradation of organic compounds leads to the formation of carbon dioxide and water, photoactive compounds can be transformed into more persistent compounds under ambient irradiation conditions. Games et al. [
18] stated that in their experiments using radiolabelled octadecyltrimethylammonium chloride, no stable intermediates were formed. More recent evidence [
10] revealed that the biodegradation of diol/triol quaternary ammonium salts proceeds due to the fission of C–N bonds, resulting in aldehydes and nitrogen derivatives without the formation of resistant intermediates. The aldehydes are oxidized to the respective carboxylic acids to be readily biodegraded via beta-oxidation to water and carbon dioxide [
19,
20]. Formaldehyde resulting from the cleavage of a methyl group is biodegraded by many metabolizing microorganisms. The tertiary amines formed are also readily biodegradable, as shown by Yoshimura et al. [
21]. Moreover, it has been noticed that the results from some screening tests tend to underestimate the biodegradation potential of esterquats in the marine environment. It has been proposed that readily biodegradable quaternary ammonium salts will not accumulate in the most ecosystems. This statement has been confirmed by the half-life period of octadecyltrimethylammonium chloride, which is 2.2 days in river water [
22]. The half-life period of the similar alkyltrimethyl quaternary ammonium salt in seawater is 6 days [
23].
UV-spectrophotometry is a suitable analytical technique of choice in research and industrial laboratories due to its inherent simplicity, portability, and low cost [
27]. The principles of UV-spectrophotometry were applied for the determination of cationic surfactants using azo dyes in acidic or basic mediums [
28,
29,
30,
31,
32]. In the case of esterquats, the development of a sensitive and simple method for the quantification of the complex systems with several active ingredients still constitutes a major challenge.
The aim of the present study is to investigate the rate of FLOT 2015 desorption via seawater and probable mechanism of its chemical degradation with the aid of a simple and adequate UV-spectrophotometric method. By investigating the desorption characteristics of the adsorbed collector FLOT 2015, important information regarding its mobility and stability could be obtained that would be valuable for environmental impact assessment.