Movement and accumulation of ions across a membrane against their concentration gradient can be explained by

Movement and accumulation of ions across a membrane against their concentration gradient is explained by active transport. Active transport is carried out by specific membrane proteins.
(2) Osmosis is the movement of watermolecules from an area of high water concentration to an area of low water concentration across a selectively permeable membrane. It is a passive process and does not require energy expenditure.
(3) Facilitated diffusion is a type of passive transport that involves the movement of molecules or ions across a membrane from an area of higher concentration to an area of lower concentration, with the help of specific embrane proteins called transporters or channels. 
(4) Passive transport refers to the movement of molecules or ions across a cell membrane from an area of higher concentration to an area of lower concentration, without the use of energy. This process occurs spontaneously, driven by the concentration gradient.