Potassium and calcium content in padelegan water which is used as the raw water for making salt

Potassium and calcium are elements contained in seawater. The presence of potassium and calcium in raw saltwater were impurities in producing non-food salt. On the other hand, potassium and calcium as target minerals are desirable in mineral-rich healthy salt (food salt) production. Information about the potassium and calcium content in raw salt water can assist in analyzing the quality of the salt to be produced. The purposes of this study were; to determine the content of potassium, and calcium in Padelegan waters used as a source of salt raw materials, compare them with other locations, and their correlation with water quality. The potassium and calcium content in the sample were determine used the AAS (Atomic Absorption Spectrophotometry) method. Potassium concentrations ranged from 221,870 to 285,110 mg/L, and those for calcium from 497,700 to 552,713 mg/L. The potassium content in Padelegan waters is smallest than other reference waters. In contrast, the calcium content in Padelegan waters is greatest than in other reference waters.


Introduction
In nature, seawater contains various elements [1].Almost all elements in the periodic table of elements are contained in seawater [1][2][3][4].Due to the abundance and diversity of elements contained in seawater, seawater is widely used as mining minerals [5,6], as raw materials for making salt [7], as raw materials in CAP (Chlor Alkali Plant) [8], and produce fresh water by desalination [9].This reason makes seawater a source of energy and commercial value if appropriately managed.
Based on the content and resident time, elements in seawater are classified into three categories: major, minor, and trace elements [10].Calcium (Ca 2+ ) and Potassium (K + ) are some of the significant metals in seawater.Calcium occupies the third position and potassium fourth based on the abundance of cations in seawater [11].In the production of salt raw materials, calcium and potassium derived from salt raw materials are by-products and impurities produced from salt ponds.Due to raw materials target high NaCl yields and low impurities in the production of salt, thus making the calcium and potassium content in salt undesirable.
Studies on the calcium content in raw water, brine, and salt from the land of PT Garam Pamekasan have been carried out by Rohma et al. [12].However, studies on calcium and potassium content in raw water in Padelegan waters have never been done before.This paper will discuss the content of calcium and potassium in raw water from Padelegan waters which are used as raw material for making salt, compare their concentrations with other waters, and their relationship with water quality parameters.Based on this, the information provided in this paper is a preliminary study in assessing raw water quality for producing raw material salt.

Study Area
The research location is located in Padelegan Waters at coordinates 7°14'19.41"S-7°14'10.86"Sand 113°31'52.72"E-113°31'58.87"E.Padelegan waters are adjacent to Padelegan Village in Pademawu District, Pamekasan Regency.Padelegan waters are used as raw salt water by smallholder salt farmers around Padelegan and salt farms at University of Trunojoyo-Madura (UTM).Raw water is obtained from the Madura Strait (Padelegan waters) by flowing raw water into ponds when the high tide.On the east of Padelegan water, a mangrove ecosystem is also a tourist spot for tourists.While on the west side, there is a salt pond managed by the Padelegan community.On the side of the Padelegan beach, directly opposite the UTM salt pond, the community uses it as a beach resort known as The Legend beach.

Field Sampling
The field investigations and water samplings were conducted on August 9, 2022.The water samples were collected from three stations (figure 1).Station 1 is located at the UTM salt pond raw water entrance, station 2 is located in the pond canal water body, and station 3 is in the coastal area of Padelegan.Water sample collection was carried out when the waters were experiencing high tide, and each point was repeated 3 times.Pre-cleaned dipper was used to collect water samples.Temperature and dissolved oxygen (DO) was measured using eutech instruments DO600.Eutech ph 450, Turbidity Meter Lutron TU-2016, and ATAGO Hand Held Refractometer (Japan) were used to measure pH, turbidity, and salinity, respectively.In addition, each parameter was triplication measured.Polyethylene terephthalate (PET) bottles were used as water samples containers and stored in a cool box.The water samples were then taken to the laboratory to analyze the potassium and calcium content.The water quality at each station is shown in table 1.

Laboratory Analysis
Calcium levels were measured in water samples using the Atomic Absorption Spectrophotometry (AAS) method [13].Calcium analysis preparation begins with a standard solution of calcium with a concentration of 10 μg/mL.Standard series solutions were prepared using a standard solution of 10 μg/L, diluted with distilled water to obtain concentrations of 0, 2, and 5 μg/L.Sample preparation is done by filtering water samples.Then the filtered water sample was added to concentrated hydrochloric acid and lanthanum solution and diluted with distilled water.Analysis using AAS was carried out at a wavelength of 422.7 nm.The data was then made into a calibration curve to obtain the equation used to calculate the concentration of Ca in the sample.
As with calcium, potassium levels in water samples were measured using the AAS method [13].Preparation of calcium standard series solution by adding HNO3 to CaCO3 and then dissolving it using aqua dest.Next, the filtered water sample was added to hydrochloric acid until the pH was 5. Then the water sample was read for absorbance using AAS at a wavelength of 766.5 nm.The calibration curve and its equations were made based on the absorbance of the standard series solution results from the AAS analysis.Then the calibration curve equation is used to calculate potassium levels in the sample.

Statistical Analysis
Determining if there were any significant differences between three station potassium and calcium means was obtained from ANOVA (Analysis of Variance).Tukey Honestly Significance Difference (HSD) test was performed as a post hoc test after the ANOVA with α = 0.05.Correlation analysis of potassium and calcium content with water quality parameters was carried out using the Pearson Correlation Test.Performing statistical analysis and data visualization utilizing the R Programming Language.

Result and Discussion Water Quality
The temperature in the waters of Padelegan ranges from 27,667 -28,333 °C.The highest temperature is shown at station two, followed by stations one and three with respective values of 28.333 °C, 28.067 °C, and 27.667 °C.The temperature value obtained in this study is lower than Rahmadani et al. [14].Rahmadani et al. stated that the temperature in Padelegan waters ranged from 29.3 -30.0°C.The difference in temperature measurement results is thought to be due to the difference in measurement time.Measurements of temperature and water samples in this study were carried out when the waters were heading towards the highest tide, which occurred at night.Thermal absorption by the sea occurs optimally heating when daytime is compared to night due to solar radiation daytime exposure [15].Changes in the temperature of the water can affect the aquatic metabolic activity [16] and the solubility of gases in water [17].Moreover, increasing the temperature will cause organisms in the sea to often carry out respiration due to increased metabolic activity.This seawater heating causes the need for dissolved oxygen to increase and causes the dissolved oxygen concentration to decrease in line with the increase in temperature.
Dissolved oxygen levels in the study area ranged from 5,890 -7,480 mg/L.The trend of temperature distribution in Padelegan waters is inversely proportional to temperature; station three shows the highest dissolved oxygen level (7.840 mg/L) compared to the other two stations.The value of dissolved oxygen content obtained in this study is smaller than that of Rahmadani et al. [14], which amounted to 8.11 -11.37 mg/L.The difference in results is thought to be because, in this study, DO measurements were carried out at night.At night, producers as phytoplankton [18,19] and marine plants do not carry out photosynthesis due to the absence of sunlight [20].As a biological process, photosynthesis produces oxygen as the product.Furthermore, photosynthesis does not occur at night, causing a decrease in water DO levels [18][19][20].
The field measurements showed that the pH value at the study site ranged from 7.910 -8.137.The range of pH values in this study is similar to the pH values obtained by Rhamadani et al. [14]; the pH in Padelegan waters ranges from 7.68 -8.11.Occurring of ocean acidification could indicate by seawater pH value.Furthermore, the water's pH variability can be caused by water dynamics such as tides and ocean currents [21].
The range of salinity values in Padelegan waters is 30,333 -33,333 ppt.The highest salinity level was shown at station three (33,333 ppt), and the lowest was at station two (30,333 ppt).The difference in salinity at the three stations is due to the station's location.Station three is located on the coast and interacts directly with the waters of the Madura strait, which causes station three to have the highest salinity value.Station one, located at the water gate of the UTM salt pond, is semi-closed because there is a bulkhead for the salt pond canal around the floodgate, and only one channel is open to the northwest.The location of station one causes this station to be semi-closed and minimizes the decrease in salinity except during the rainy season.The location of station two is at the junction of the central canal of the salt pond, settlements, and mangrove ecosystems.The location of station two is thought to cause the salinity to be the lowest compared to other stations because it allows freshwater runoff from residential areas to station two.
The turbidity of the research location ranged from 12.49 to 41.73 NTU.The largest turbidity is shown at station three with a value of 41.73 NTU, then station one (18.423NTU)and station two (12.49NTU), respectively.The range of turbidity values from the results of this study is higher than the results of previous studies, which ranged from 4.08 to 29.82 NTU [22].The high turbidity value is because, at the time of measurement, the waters of Padelegan were heading toward the highest tide and high waves.The dynamics of the waters in the form of tides and waves cause turbulence and agitation of sediment at the bottom of the water, causing the turbidity value of the water to be high.Karimpour et al.; Baeyens et al [23,24].

Calcium and potassium content
Figure 2 reveals calcium and potassium content in water at three stations of Padelegan.The bar followed by the same letter indicates insignificant differences between mean values according to the Tukey HSD test.Generally, both minerals show a similar trend where the closer the sea, the smaller the concentration.
Station one has the highest calcium content compared to other stations, with a value of 552,713 mg/L, followed by station two with 513,980 mg/L and three with 497,700 mg/L (Figure 2).Furthermore, based on the results of the Tukey HSD test, the average calcium content of station one was significantly different from stations two and three at P<0.05.Meanwhile, the average calcium content at stations two and three did not differ significantly.The high calcium level at station one is thought to be due to optimally concentrated raw water from exposure to sunlight and wind.Furthermore, the concentrated raw water is not affected by oceanographic dynamics such as currents and waves because of its semi-enclosed location.The location of station one is at the sluice gate on the UTM salt pond canal, thus making station one a semi-closed location and minimally affected by the dynamics of seawater movement.As one of the major elements in the sea on alkaline earth, calcium is included in the second class of highly reactive elements, also known as aquatic nutrients.Calcium plays a role in the biosynthesis of the tissues of marine organisms such as phytoplankton and zooplankton.In addition, the mineralization of calcite as a skeleton and shell formation in marine organisms (invertebrates) also requires calcium as the main element [25].Sources of calcium from marine waters come from metal carbonates and evaporites, while sources of calcium that enter the sea can come from river inputs, groundwaters, and oceanic crust [11,[25][26][27], then added another source of calcium derived from dolomite which reacts with carbon dioxide and water with the following equation: Ca, Mg(CO3)2 + 2CO2 + 2H2O → 2Ca 2+ + 2Mg 2+ + 4HCO 3- (1) According to Tukey HSD test result (P<0.05), the average potassium content the three stations showed a significant difference.The highest average value of potassium content is shown at station one, 285.11 mg/L (figure 2).At the same time, the third station showed the smallest value of potassium content (221.87 mg/L) compared to the three stations.The potassium content values trend decreased at stations facing the sea (station three) and increased at stations far from the sea and semi-enclosed (station one).As with calcium, the high potassium content at station three is thought to be due to its location close to settlements, allowing for potassium runoff from human activities.Sources of potassium can come from fertilizer waste used in farming [25].
Furthermore, other sources of potassium that can enter sea waters are added from rivers and groundwater [25].In contrast to calcium, potassium is one element included in poorly reactive elements [25].A poorly ractive element means that potassium has a total resident time.However, potassium can react with colloidal and clay particles that enter the sea via river [11].
Seawater from Padelegan waters is used as raw material for making salt by smallholder salt farmers and UTM salt ponds.The value of calcium and potassium content in raw water will affect the quality of the salt produced.In the manufacture of salt as raw material for caustic soda, iodized consumption, and various food industry salts, calcium and potassium are undesirable elements of impurity.The salt decomposition requires a high NaCl content of> 94% so that the presence of high calcium can reduce NaCl levels in salt.water samples Figure 3 provides a bar graph of the ratio of calcium and potassium in Padelegan Waters to 4 other water areas.Figure 3.a.showed calcium levels in Padelegan waters were higher than in Great Cumbrae [28], Mediterranean [9], Singapore [29], and Taiwan waters [30].The four comparison locations had calcium levels below 500 mg/L, while the average calcium level in Padelegan was around 550 mg/L.In contrast with calcium, the potassium content in Padelegan shows the lowest value compared to other waters (Figure 3. b).Furthermore, it is added that Singapore's potassium value is twice as significant as that of Padelegan.where potassium and calcium have a weak negative correlation with an r = -0.59[ 32].The level of DO and temperature showed a weak negative correlation with calcium and potassium concentration.However, weak positive correlations were discovered between temperature and pH with calcium and potassium concentration.

Conclusion
The aims of this research were; to determine the potassium and calcium content in Padelegan waters used as a source of salt raw materials and compare them with other locations.Padelegan potassium concentrations ranged from 221,870 to 285,110 mg/L, and those for calcium from 497,700 to 552,713 mg/L.The result shows that potassium content in Padelegan waters is smaller than in other reference waters.In contrast, the calcium content in Padelegan waters is greatest than in other reference waters

Figure 2 .
Figure 2. The graph showed the concentration of calcium and potassium from three stations'water samples Figure3provides a bar graph of the ratio of calcium and potassium in Padelegan Waters to 4 other water areas.Figure3.a.showed calcium levels in Padelegan waters were higher than in Great Cumbrae[28], Mediterranean[9], Singapore[29], and Taiwan waters[30].The four comparison locations had calcium levels below 500 mg/L, while the average calcium level in Padelegan was around 550 mg/L.In contrast with calcium, the potassium content in Padelegan shows the lowest value compared to other waters (Figure3.b).Furthermore, it is added that Singapore's potassium value is twice as significant as that of Padelegan.

3rdFigure 3 .
Figure 3.The figure showed the comparison of calcium (a) and potassium (b) concentration in Padelegan waters with other areas, including Great Cumbrae, Mediteranian, Singapore and Taiwan.The red dashed lines were exhibited as calcium and potassium in Padelegan waters.Pearson correlation was performed to determine the correlation between calcium and potassium content on water quality in Padelegan waters.The results of the Pearson correlation test are shown in table 2. It illustrates calcium and potassium, each other has a strong positive correlation (r= 0.901, P<0.01).These results are similar to Fianko et al., who got similar results; potassium and calcium had a positive correlation with a value of r=0.73[31].However, Assemian-Niango et al. get different results where potassium and calcium have a weak negative correlation with an r = -0.59[ 32].The level of DO and temperature showed a weak negative correlation with calcium and potassium concentration.However, weak positive correlations were discovered between temperature and pH with calcium and potassium concentration.

Table 1 .
Water quality of each stations in Padelegan Waters.

Table 2 .
Pearson correlation coefficient of calcium and potassium concentration with water quality