Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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A Review on Alkalinity Analysis Methods Suitable for Korean Groundwater

우리나라 지하수에 적합한 알칼리도 분석법에 대한 고찰

  • Kim, Kangjoo (Department of Environmental Engineering, Kunsan National University) ;
  • Hamm, Se-Yeong (Division of Earth Environmental System, Pusan National University) ;
  • Kim, Rak-Hyeon (Department of Soil and Groundwater, Korea Environment Corporation) ;
  • Kim, Hyunkoo (Soil and Groundwater Division, National Institute of Environmental Research, Environmental Research Complex)
  • 김강주 (군산대학교 환경공학과) ;
  • 함세영 (부산대학교 지구환경시스템학부) ;
  • 김락현 (한국환경공단 토양지하수처) ;
  • 김현구 (국립환경과학원 토양지하수연구과)
  • Received : 2018.11.05
  • Accepted : 2018.12.11
  • Published : 2018.12.28
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Abstract

Alkalinity is one of the basic variables, which determine geochemical characteristics of natural waters and participate in processes changing concentrations of various contaminants either directly or indirectly. However, not a few laboratories and researchers of Korea still use alkalinity-measurement methods not appropriate for groundwaters, and which becomes one of the major reasons for the poor ion balance errors of the geochemical analysis. This study was performed to review alkalinity-measurement methods, to discuss their advantages and disadvantages, and, thus, to help researchers and analytical specialists in analyzing alkalinity of groundwaters. The pH-titration-curve-inflection-point (PTC-IP) methods, which finds the alkalinity end point from the inflection point of the pH titration curve are revealed to be most accurate. Gran titration technique among them are likely to be most appropriate for accurate estimation of titrant volume to the end point. In contrast, other titration methods such as pH indicator method and pre-selected pH method, which are still commonly being used, are likely to cause erroneous results especially for groundwaters of low ionic strength and alkalinity.

알칼리도(alkalinity)는 물의 화학적 특성을 결정하고, 각종 오염물질의 거동에 직간접적인 영향을 주는 중요한 기본 변수이다. 그러나, 적지 않은 실험실과 연구자들이 적절하지 못한 분석법으로 지하수의 알칼리도를 분석하고 있으며, 이것이 불량한 이온균형오차를 야기하는 큰 이유가 되고 있다. 본 연구는 현재까지 보고된 알칼리도분석법들을 조사하고 그 장단점을 분석함으로써, 지하수 알칼리도 분석을 수행하는 실험실이나 분석자들에 도움을 주기 위한 목적으로 수행되었다. 본 연구를 통하여 pH적정곡선의 변곡점으로 알칼리도 적정 종점(end point)를 찾는 방법이 가장 정확도가 높음을 알 수 있었다. 그 중에서도 Gran적정법이 종점까지 적정한 용액의 부피를 정확히 산출하는데 가장 적절한 것으로 조사되었다. 반면, 현재에도 여전히 많이 이용하고 있는 pH지시약을 이용하여 적정하는 방법이나 미리 정해진 pH를 종점으로 하여 적정하는 방법은 묽거나 알칼리도가 낮은 지하수의 분석에는 문제가 있는 것으로 판단된다.

Keywords

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Fig. 1. Bjerrum diagram for dissolved CO2 species at closed system. This figure shows that the alkalinity end point where [H+] = [HCO3-] changes according to DIC.

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Fig. 2. The relation between alkalinity end point and pH titration curve. End point exactly matches with the inflection point of pH titration curve at pH between 4 and 5. This diagram was prepared with the DIC condition of 5.4 mmol/L and pCO2 of - 1.0.

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Fig. 3. An illustration of Gran titration method based on actual data.

Table 1. Alkalinity values (meq/L) of Korean groundwaters measured using the Gran titration technique

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Table 2. Methods for alkalinity measurements

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Table 3. Estimation of alkalinity contribution from various components indicated in Standard Methods (APHA et al., 2012a)

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Table 4. The pH ranges for color changes of various pH indicators used for alkalinity measurements

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Table 5. End-point pH values suggested by Standard Method (APHA et al., 2012a)

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