Rapid industrialization has led to the creation of large amounts of wastewater containing various pollutants, among which heavy metals stand out. Heavy metals such as Cd (II) ions cause serious chronic diseases and even death if they are present in high concentrations. Therefore, this manuscript investigates the possibility of Cd (II) ion removal by precipitation method using Ca(OH)2. In order to optimize the precipitation process, the following were investigated: initial pH, initial concentration of Cd (II) ions, dose of added Ca(OH)2, stirring speed and contact time, as well as the influence of competing ions on the removal efficiency of Cd (II) ions. The optimization of the precipitation process was performed by varying one operational parameter at a time, while keeping all other parameters constant. Results of Cd(II) ion removal efficiency and optimal conditions are: pH 5 (99.961%), stirring speed of 0 rpm (99.985%), contact time metal-precipitant 5 minutes (99.965%), added dose of Ca(OH)2 60 mg (99.965%). Complete removal of Cd (II) ions was achieved at a Cd(II) ion concentration of 10 ppm, and high removal efficiency was achieved at concentrations of 50-300 ppm (98.231-99.994%). The removal efficiency of over 99% of Cd (II) ions was achieved during individual tests of ion competitiveness. Therefore, it can be concluded that under the tested conditions, Ca(OH)2 is an effective agent for removing Cd (II) with an efficiency above 99%.

New accurate, precise, and sensitive spectrophotometric method were developed for the assay of L-ascorbic acid in pharmaceutical preparations. The determination of L-ascorbic acid was based on its oxidation by potassium peroxydisulfate in the presence of Ag(I) as a catalyst. The molar absorptivity of the proposed method was found to be 8.61 · 103 L mol-1 cm-1 at 248 nm. Beer's law was obeyed in the concentration range of 0.46–20.0 μg mL–1. Other compounds commonly found in vitamin C and multivitamin products did not interfere with the determination of L-ascorbic acid. The proposed method was successfully applied for the determination of L-ascorbic acid in pharmaceutical formulations. The results obtained with the proposed method showed good agreement with those given by the titrimetric method using iodine.

In addition to soda, the Solway production process yields large amounts of waste sludge that contains a high percentage of CaCO3 and Ca(OH)2. In this paper, solid waste sludge from a soda factory in Bosnia and Herzegovina of a certain granulation was used to remove metal ions from the binary system initial concentrations of 500 mg/L. The research results showed that the precipitation efficiency for the binary system Cu - Ni was 99.810% at a pH of 11.42 for Cu2+ and 99.896% for Ni2+ at a pH of 10.86, while for the binary system Pb - Zn it was 99.84% at the same pH value of 10.64. This research has shown that it is very difficult to separate and remove metal precipitation from binary systems because the optimal pH for one metal does not correspond to another metal.

: The hydroxide precipitation method, using NaOH as a precipitant agent, was conducted to treat synthetic monocomponent and two-component water solutions of Pb 2+ and Zn 2+ with initial concentrations of 50 and 500 mg/l of each metal. The effect of pH and initial concentration of lead and zinc ions on their removal were investigated. The precipitation experiments were carried out by batch method that involves the mixing of NaOH with solutions containing metal ions to occur nucleation, solid growth and subsequent separation of precipitates from solution by filtration. The results showed that the removal efficiency was increased by increasing of pH and initial concentration of metal ions in their water solutions. Hydroxide precipitation method using NaOH is an ef-ficient technique for the removal of lead and zinc ions from their monocomponent and two-component water solutions of different concentrations, with maximum removal efficiency in the pH range of 10.32 to 11.39.

Two new, accurate, precise, and sensitive spectrophotometric methods were developed for the assay of L-ascorbic acid in pharmaceutical preparations. The determination of L-ascorbic acid was based on its oxidation by potassium peroxymonosulfate (method A) and hydrogen peroxide in the presence of Cu(II) as a catalyst (method B). The molar absorptivities were found to be 1.48×10 and 1.06×10 L mol cm for methods A and B, respectively. Beer's law was obeyed in the concentration range of 0.65–11.20 μg mL for method A and 0.51–16.00 μg mL for method B. Other compounds commonly found in vitamin C and multivitamin products did not interfere with the determination of L-ascorbic acid.. The proposed methods were successfully applied for the determination of L-ascorbic acid in pharmaceutical formulations. The results obtained with the proposed methods showed good agreement with those given by the titrimetric method using iodine.