Calling select stored procedure using Entity Framework in ASP.NET MVC 5

I am calling my stored procedure through the following code:

var DepartmentList = db.Database.SqlQuery<Department>("DpDemoProcedure @iHandle",
       new SqlParameter("@iHandle", "GeDepartment"));

However, I am getting this exception:

The SqlParameter is already contained by another SqlParameterCollection.

This is my stored procedure:

CREATE PROCEDURE DpDemoProcedure
    @iHandle VARCHAR(50) = NULL
AS
BEGIN
    SET NOCOUNT ON;

    IF @iHandle = 'GeDepartment'
    BEGIN
        SELECT * 
        FROM Departments 
        ORDER BY DepartmentName 
    END     
END
GO

I am getting confused where exactly my code working wrong. I am new to Entity Framework.

This my action method where I am returning value

public ActionResult Demo()
{
    var DepartmentList = db.Database.SqlQuery<Department>("DpDemoProcedure @iHandle",
           new SqlParameter("@iHandle", "GeDepartment"));

    return View(DepartmentList);
}

I am using this list for display purpose

@model IEnumerable<MediorbitMain.Department>
@{
    ViewBag.Title = "Demo";
    Layout = "~/Views/shared/_Layout.cshtml";
}

<h2>Demo</h2>

<table>
    <tr>
        <th>DepartmentId</th>
        <th>DepartmentName</th>
    </tr>
    <tbody>
        @foreach (var item in Model)
        {
            <tr>
                <td>@item.DeptId</td>
                <td>@item.DepartmentName</td>
            </tr>
        }
    </tbody>
</table>