Adsorption process is a key reaction that controls the bioavailability and mobility of arsenic in the environment. So far, studies regarding As adsorption to minerals in multiple component systems are still limited. In this study, we investigated the effect of Ca2+ as the major cation and PO 4 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq143.tif"/> as the major anion on As(III) or As(V) adsorption at goethite-water interface over a wide pH range. Data of the adsorption experiments were compared to those calculated with the CD-MUSIC model. Results show that Ca2+ promoted As(V) adsorption at high pH, but slightly influenced (increased or decreased) As(III) adsorption. Phosphate competed strongly with the adsorption of both As(III) and As(V), especially at relatively low pH for As(III) and high pH for As(V). The combined effect of Ca2+ and PO 4 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq144.tif"/> on As adsorption results in an increased As(III) adsorption with the increase of pH (3–10), whereas for As(V) a maximum adsorption can be seen around pH 6. The CD-MUSIC model can predict As adsorption in the complex systems by considering electrostatic interactions and site competition. Competition with PO 4 3 − https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351046633/8978195a-ffaa-498f-8e06-bee4769ddb72/content/eq145.tif"/> leads to a decrease of the bidentate As(III) and As(V) surface species. Our results can provide understanding needed in the risk assessment and remediation of As contaminated soils and water.